Zola: Tristan doing everything right to earn West Ham stay
"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.
"I haven't spoken to him but I believe he wants to stay."
Tristan 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.