The France midfielder arrives from Olympique Marseille.
"He will surprise one or two, he's a good player, a Champions League-quality player," Clarke said.
"I think he's probably a name not many people knew about or thought of. I've seen him over a number of years going into Europe and watching games.
"He's a player who works hard and is very good technically, understands his position and hopefully he can be a good surprise.''
For the big stories and the banter follow us on Twitter: @tribalfootball