Tristan, 33, is out of contract at the end of the campaign and has two goals in three appearances while playing for his future at the club.

"Obviously he has put himself in a strong position," Zola said.

"I think he is playing for his future, but more than that I would say he is playing because he is enjoying it.

Zola feels West Ham are now seeing the best from Tristan after he arrived six months ago and took time to build his match fitness.

"The problem with Diego was the physical condition," Zola said. "When he first came here in November he wasn't as good as now physically.

"Other than that Diego Tristan has got everything and he can be a top striker in Europe easily.

"Don't forget he has been a national player for Spain and has been top scorer in that country for many years.

"He just lost a little bit of it in the last few years but he is getting back very, very quickly and in the last few games he has been outstanding.

"The way he played against Chelsea and against Stoke City was quite remarkable."

Zola will also consider keeping on David di Michele, also 33, who has been on loan from Italian side Torino.

"That is something that we will consider," Zola said.

"I played until I was 39. If somebody looks after themselves well it's not a problem at all."