Roberto did little to convince supporters when he shipped four goals in the Carabao Cup defeat at League One Oxford last month.

But Pellegrini has no doubts about the experienced shot-stopper and insists West Ham are in safe hands.

The Hammers boss said: "Of course last season Lukasz was one of our best players and one of the best goalkeepers in the League.

"He continued this season in the same way but unfortunately for him and for the team he is injured.

"We brought Roberto in and we have the same trust in him as with Lukasz. He's a goalkeeper with an important career with big teams. I am absolutely sure he will replace Fabianski in the way we know he is able to.

"I don't think the supporters have any doubt about Roberto. Against Oxford we had a very bad performance, but not because of him.

"I see him working every day and everyone, especially the fans, must trust in him."

West Ham head to Everton on Saturday, the scene of their first Premier League win under Pellegrini after they began last season with four straight defeats.

Andriy Yarmolenko scored twice that day, but a few weeks later he was ruled out for the rest of the campaign with an Achilles injury.

The £17.5million winger has begun this season with a bang, finding the net three times already, while he was also on target for Ukraine against Portugal in midweek.

"I'm so happy for him that not only is he playing, but he has also scored for our squad and for Ukraine," added Pellegrini.

"I think he also had a very good game, and I hope that he will continue at the same performance level with us.

"We must be careful with him because he cannot play a lot of games in a row because he's just coming back from a season where for nine or 10 months he couldn't play.

"But I am sure that he will be an important player. That's why we bought him."