The Frenchman made his first appearance of the season in Thursday's 2-2 Europa Conference League draw with Rennes, having asked to leave the club before the campaign started.
The club's record buy has been inconsistent since his £60million-plus move from Lyon two years ago and found himself frustrated at being left out of the side by interim boss Ryan Mason at the end of last season.
"They have an amazing squad, talented players, they play good football, they are organised, they are intense. They are European champions so we must value that as we do to all of the opponents but Sunday we will compete, that's a promise.
"No, there's no surprise at all. Thomas already did an amazing job at Borussia Dortmund (and was) fantastic at PSG. He and his coaching staff have enormous quality so I am not surprised by the success of Thomas.
"For me it is not a surprise because you can see how good they play."