Frank Lampard insists Mason Mount is as important to him at Chelsea as he was at Derby County.
Mount moved back to Stamford Bridge with Lampard last summer and has made 44 appearances across all competitions.
Despite being dragged at half-time in Sunday's win over Leicester, the 21-year-old remains an important figure in Lampard's side.
Speaking ahead of Wednesday's clash with West Ham, the Englishman said: "I rely on Mason a lot. I did at Derby, I do at Chelsea.
"He brings so much to the team in his work ethic and the way he can start the press in midfield and obviously his quality on the ball which is only going to get better and it's already at a high level.
"Mason wouldn't have been happy to come off at half time. I know that from myself and if there's one comparison I can make is that I know if he's not playing, then he won't be happy.
"He should not be happy that evening, but then straight back to it afterwards because he knows how much I trust in him and he works brilliantly every day.
"When I say Mason, I mean Billy [Gilmour] and Reece [James] in the same breath because they show a similar attitude. There will be no problem with Mason because it was a one-off game, I had to make a decision and it doesn't affect my thinking for West Ham or going forwards.
"I think the first two games after the restart, which Mason played 90 minutes in both, at Aston Villa he was incredibly lively with the ball, gave them a lot of problems going forward, probably unfortunate not to score or have an assist.
"The work ethic and quality that he showed against Manchester City was also incredible and the performance we showed as a team was also really good.
"So, he had two big performances in a week and then in the Leicester game; Mason didn't really have a bad performance, it was a performance in line with the team and my choices to change were about the players that I could bring into that performance rather than the players who were on the pitch, because I could have made a lot of changes in that game.
"It was more about whether I could bring some energy into the team."
