Nasri, who had been training with the Hammers for a month, played his first match in more than a year when he started the FA Cup victory over Birmingham last weekend.

The 31-year-old put in an impressive 60-minute display and Pellegrini – under whom Nasri won the Premier League title with Manchester City – is confident he can recapture his best form.

Pellegrini also believes Nasri has a point to prove following his suspension.

"He wants revenge, about the ban of 12 months or more, to decline his career," said Pellegrini.

"From Arsenal, then City bought him. From there his career declined, without doubt.

"I think we can expect a lot from him because he is a top player. He continues having some minutes, and when he is used to playing 90 minutes again he will be a top player at this club."

Pellegrini may currently be having issues with wantaway striker Marko Arnautovic but he insists the signing of Nasri, another player with a reputation for being difficult to handle, was a gamble worth taking.

"Every time you choose a player you have a risk without any doubt. Sometimes when you invest more money your risk increases," Pellegrini added.

"When I bring players here I say my responsibility doubles than when players were already here with the squad.

"You must take decisions. This was a risky decision, but not a high-risk one because he signed for six months.

"He made no problem with the contract. He was not fighting for more or less money. He wants to demonstrate between now and June that he is able to be a top player in football."

West Ham will be without centre-half Fabian Balbuena for up to two months after the Paraguayan underwent knee surgery.

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