Manuel Pellegrini believes Samir Nasri can recapture his best form with West Ham after joining on a free transfer.
The 31-year-old midfielder signed for the Hammers earlier this week after completing an 18-month doping ban.
Nasri was an unused substitute against Brighton in midweek and is expected to make his debut against Birmingham in the FA Cup on Saturday.
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The Frenchman was an integral part of Pellegrini's title-winning Manchester City side in 2014 and the Chilean is confident he can hit the heights again.
"He has been training with us for a month, he is looking very well, he lost weight," Pellegrini said.
"And I think that football is like when you ride a bicycle when you are a small boy, you never forget.
"Samir is a very technical player and I am sure he will play in the same way as he did before. I trust in him a lot.
"I suppose because he knows that this is revenge for him, he is motivated, working hard and he has a lot of quality and I am absolutely sure he will be a player that makes a difference."
Nasri was banned for a breach of anti-doping rules when, as a Sevilla player, he used drip treatment in 2016.
"I don't want to talk about whether it was his fault or not his fault. He was involved," Pellegrini added.
"I have known Samir Nasri since I was at Manchester City. He was a top player in the first year, one of the reasons we won the title was because of him.
"After speaking to him for a long time about what he was thinking about for the future, I decided to give him an option here at West Ham.
"He worked very hard to be considered and now that's why he has signed his contract and now he has to demonstrate it on the pitch. But mentally, he is another player with a lot of experience.
"That part of his life, for Nasri it has passed."
Pellegrini also confirmed that midfielder Jack Wilshere is still "some weeks" away from a comeback due to an ankle injury.