Trippier, 29, joined Los Rojiblancos from Tottenham Hotspur in July on a three-year contract and has been a frequent fixture under new manager Diego Simeone.
“I've played against him a few times now and he's so good at just picking up those little pockets of space. Before Barcelona have made three passes, he already knows where the ball's going.
"It's amazing how clever he is. Even when he's walking like that, you've always got to be aware. He's unbelievable, the best ever."
It will be Trippier's first time facing Barcelona since he arrived in La Liga, and the Guardian's Sid Lowe gave the right-back a glowing assessment several months into his Spanish transition:
Trippier was part of the Tottenham team that finished as runners-up to Liverpool in last season's UEFA Champions League, when the north London outfit met Barcelona twice during the group stage. Spurs lost 4-2 at home but managed to take a 1-1 draw in their visit to the Camp Nou.
The former Burnley man compared Messi's patient approach against that of another lightning-quick star he's had to face in recent months:
“You play against (Liverpool's) Sadio Mane, for instance, and if you take your eye off him for a second, he'll just dart in behind you.
"But with Messi, you look four times and he's still there. It's weird. A lot of the time he just walks and walks—and then, before you know it, it's a goal."
It's nothing new for fans at the Camp Nou, who have been treated to Messi's consistent class for more than a decade:
Messi looks like the favourite to win the 2019 Ballon d'Or, which would crown his sixth such accolade and make him the most successful player in the award's history (one ahead of Cristiano Ronaldo).
Barcelona president Josep Maria Bartomeu echoed Trippier's words of praise in the buildup to Sunday's clash at the Wanda Metropolitano:
Trippier will have his hands full attempting to keep Messi quiet, with Antoine Griezmann and Luis Suarez in line to start after Ousmane Dembele came off injured during Wednesday's 3-1 win over Borussia Dortmund.
Atletico's surging Englishman clearly has huge respect for Messi, but he'll put those sentiments to one side on Sunday when he'll hope to beat Barcelona for the first time in his career.