1 Player Atletico Madrid Will Regret Not Signing in 2015 Summer Transfer Window

Atletico Madrid and coach Diego Simeone had a tough task over the summer. Following the departures of key players like Arda Turan, Mario Mandzukic and others, Atletico's squad needed an overhaul. But despite the difficulty of the problem, Simeone managed quite well, arguably making his side stronger than it was before by making a series of shrewd signings.

As such, second-guessing Atletico's transfer dealings during the most recent window is almost unfair. But if forced to pick one player that Simeone might regret not signing this summer then it would have to be Antonio Rudiger.

Francisco Seco/Associated Press

First, though, let's examine just how well Atletico and Simeone performed in the market. 

Turan's move to Barcelona represented Atletico's biggest loss of the summer, but the midfielder brought the club €34 million (plus a potential €7 million more in add-ons), according to ESPN FC. Other key losses included Mandzukic and Raul Jimenez, both forwards, as well as defender Toby Alderweireld and midfielders Mario Suarez and Raul Garcia.

To offset the departures Simeone brought in—among others—forwards Jackson Martinez and Luciano Vietto and midfielders Matias Kranevitter and Bernard Mensah. Defenders Filipe Luis and Stefan Savic were also signed in the summer.

Simeone's dealings this summer have generally drawn praise from the media. At World Soccer Talk, Terrance Ross ranked three of Atletico's summer signings—Luis, Martinez and Vietto—in his top 10 La Liga moves of the summer. Here at B/R, Karl Matchett gave Atletico an overall transfer-window grade of A-, while Sam Tighe gave Los Colchoneros a high rating among Europe's elite:

So, how does Rudiger fit into all of this?

A 22-year-old Germany international, Rudiger was available for a transfer from Stuttgart over the summer. In July, Sky Deutschland (h/t Marca) linked Atletico with a move for the defender as Simeone looked to bolster his defense following the departure of Alderweireld. As Marca noted, Rudiger is a "solid defender with a strong physical presence." Thus his style would have fit well with Simeone and Atletico.

JAVIER SORIANO/Getty Images

No deal ever materialized, and instead Atletico signed Savic from Fiorentina, sending Suarez the other way. Rudiger joined Roma on loan, though the Italian club can exercise an option to make the deal permanent ahead of the 2016-17 season, per ASRoma.It.

In his analysis of the transfer, B/R's Tim Collins noted that Savic is strong in the air but weak in the areas of power and speed. At Simeone's Atletico, it's unusual to see a defender who lacks elite power and speed. As Matchett wrote in his grading of the club's summer transfers:

"

Savic is a departure in terms of style from Atleti's usual centre-backs; he is much more agile and quick-footed rather than aggressive and uncompromising. It remains to be seen whether he'll fit in with the defend-at-all-costs approach that Josema Gimenez and Diego Godin display—he hasn't yet featured in La Liga.

"

That might not be a huge problem. Atletico's first-choice back four is superb, and Los Colchoneros will be a strong defensive team this season. But if Godin or Gimenez come down with an injury, Savic will have to step in.

Marco Vasini/Associated Press

Admittedly, Savic is a solid replacement for Alderweireld. His positioning, reading of the game and distribution are strengths, and at 24, he is a young player who could become a long-term contributor to the team.

Rudiger, though, is even younger and is already a full international. In addition, his strength and speed would have made him an ideal addition to Simeone's squad.

This is nitpicking, of course. Atletico did a fine job in the transfer market, and Simeone significantly strengthened his team. But if there's one area in which he could have done even better, it's at centre-back, where Rudiger would have represented a fantastic addition.