Barcelona's start to the season could hardly have gone better, with the club sitting top of the table in La Liga and still unbeaten, as well as progressing nicely in the UEFA Champions League.
The club are on track to regain the domestic title from Real Madrid if they show consistency over the second half of the campaign and pick up good results in El Clasico.
However, as a club striving to bounce back from winning no major titles last year, they could be active in the January transfer window.
The transfer market will give Barca manager Ernesto Valverde an opportunity to add a finishing touch or two to his squad, with some areas perhaps still not quite offering the depth or quality he'd hope for.
Here, we identify the best and worst moves the Camp Nou club could make in January, covering both players arriving and leaving.
Best: 4. Ditch Arda Turan
It will surprise nobody if midfielder Arda Turan is sold in the winter market, given he is so far down the list for Valverde—he's yet to play a single minute this term.
The Turkey international hasn't even been on the bench since the opening league game of the campaign, despite Barcelona now playing a system more similar to that which mirrors his old club, Atletico Madrid.
Valverde doesn't appear to want him at the club and a departure—ideally a sale, but a loan if needed instead—seems inevitable.
Galatasaray have been heavily linked with a move, especially after comments from former team-mate Ergun Penbe, per Fanatik (h/t the Daily Express), and it would seem to be in Turan's best interests also to agree to leave—if he has any intention of playing again, that is.
The only reason this move isn't higher on the list: If he's not in the squad anyway, what difference does it make to Barcelona if he doesn't go?
Best: 3. Bring in Leon Goretzka
Signing the right type of midfielder to play for Barcelona isn't easy. They have to be technically gifted, capable of playing under pressure and have an amount of creativity to help break down opposition teams.
The problem is those players are often expensive—so when the opportunity crops up to snare one on a reduced fee, it's wise to strongly consider the matter.
Schalke 04's Leon Goretzka is out of contract in the summer and could move in January on a reduced fee, with Barcelona one of the teams interested in his signature, per Sport Bild (h/t the Daily Mirror), and having already held preliminary talks.
He would be a good fit—capable of playing as a central midfielder in a double pivot or with the energy and tactical nous to be the right-sided interior in Valverde's fluid diamond. Goretzka also has both the physicality and the technical ability to be a success.
Best: 2. Offload Paco Alcacer
Even with Neymar gone, Ousmane Dembele injured and Gerard Deulofeu not convincing in output or consistency, Paco Alcacer still doesn't get a look-in.
He has featured a handful of times in La Liga and scored twice against Sevilla from a wing position, but he didn't get off the bench against Valencia at the weekend and hasn't played a single minute in the Champions League.
It's clear Valverde doesn't value Alcacer's offerings and, given the 24-year-old only has one role he can play in, it would be best if the club and player give the move up as a bad choice and part company.
Alcacer will still command a good price in the transfer market and can rescue his career with a couple of seasons plundering his usual dozen or so goals per season.
The one additional factor in the player's mind for a midseason move will be the 2018 FIFA World Cup; he still has an outside chance of being the alternative to Alvaro Morata for Spain, but it won't happen if he's on the Camp Nou bench.
Best: 1. Find the right forward
The best move Barcelona could make is also the trickiest one to get right, especially in midseason.
While Messi has thrived, there's perhaps another level to go up for the team: have the Argentina international as the free, central schemer—where Paulinho featured against Valencia at the weekend, at the tip of the diamond—and have another more mobile forward alongside Suarez to stretch defences.
That's not the tactic for every match, as Messi might be the better choice higher upfield with a four-man block behind him, but it has been evident that when he comes deep, there are too few runners beyond him opening up passing options.
It's also a part of the reason Suarez hasn't plundered more goals yet—when Messi roves, the former Liverpool man alone is easier to track and close out.
It won't be a big move such as bringing in Paulo Dybala—that's a potential summer transfer to work towards—but a better option than Alcacer is a must to offer more pace and direct running in the channels.
Then again, rumours of Antoine Griezmann joining Barca aren't going away, and he would be perfect.
Worst: 4. Allow a "key" backup to leave
It seems contradictory to label a non-starter a key piece of the puzzle, but depth is critical if Barcelona are to continue to challenge on both fronts, domestically and on the continent.
Part of the reason Valverde has had such a good start is his ability to switch and rest players once games are won: Denis Suarez or Deulofeu for Andres Iniesta, or Sergi Roberto and Aleix Vidal battling it out with Nelson Semedo, for example.
A handful of players are more key than others, though.
Jasper Cillessen has played just once this season but showed last year he has the ability to make it count when he's given the chance. A bad backup goalkeeper being used for a run of five or six games could have disastrous consequences—as Real Madrid are noting with Kiko Casilla.
Lucas Digne is another who hasn't played as much as his quality should suggest, and Javier Mascherano is a third.
All will be required across the course of the campaign, so letting them leave in January would be folly.
Worst: 3. Lose faith with Ivan Rakitic
The past few weeks have not been easy for midfielder Ivan Rakitic, who has been in and out of the XI and performing pretty poorly on the right side of the diamond.
Tactically, it's a change from how he has been used at Barca since his arrival in 2014, but he's more than good enough to bounce back. Right now, though, he's earning the wrath of fans and manager alike.
Valencia's goal at the weekend was in large part down to the Croatia international's failure to track the run of Jose Gaya from left-back, allowing him to overlap and cross without pressure. Valverde hauled Rakitic off soon after.
Sport reported Valverde was unhappy with both Rakitic and Semedo down the right flank—not for the first time with players on that side.
But don't write Rakitic off. He's proved regularly he's among Barcelona's most consistent and impressive all-round midfielders—a workhorse as much as an offensive threat—and he's another who will be needed as the season goes on.
Worst: 2. Offload Rafinha
While any incoming deals will mean others leave, one player Valverde should be holding on to is Rafinha.
The Brazilian has been on the injury table since April, recovering from a knee problem and yet to feature in 2017/18, but there are two reasons why the Barcelona boss should hold fire on a player he hasn't had to count on.
The first reason is a tactical one. Rafinha would be a stellar fit for the right side of the diamond shape, where the manager has had trouble finding a player to nail down a regular starting berth.
The second is the output the 24-year-old provides. He's an offensive-minded player who is both creative and capable of scoring plenty of goals when he gets a run in the team. Cutting inside on to his left foot, he's a threat from range and has previously linked well with Messi and Luis Suarez.
Fitness has been Rafinha's issue, so while a loan might be needed to get him game time, he shouldn't be sold.
Worst: 1. Sign Mesut Ozil
Like Goretzka, he's a Germany international who is out of contract in the summer; unlike Goretzka, he fails to fit the profile of a player Barcelona need in the slightest.
Ozil is tremendous in his preferred No. 10 role at opening defences in specific types of games, but he lacks the consistency at elite level and the real aggressiveness needed in a team that dominates high upfield. More importantly, he would occupy the space Messi wants to operate in.
There's no need for both of them, and there will be only one winner when deciding which player the team needs most.
Freeing up the central spaces for Messi, not clogging them up with a playmaker who won't make breaking runs from deep, should be highest on Barcelona's list of priorities for changes in the winter transfer market.