Chelsea are still unsure how long England striker Tammy Abraham will be sidelined with hip trouble.

Abraham sat out training at Chelsea’s Cobham base on Friday and will miss Saturday’s Premier League clash with West Ham at Stamford Bridge.

Lampard expects Chelsea to know by Monday the extent of Abraham’s hip issue, that he suffered in the Blues’ 2-2 Champions League draw at Valencia on Wednesday.

“We’ll know by the end of the weekend, he’s got some pain and won’t be involved tomorrow,” said Lampard.

“But then we’ll know by Monday.”

Abraham landed awkwardly on his hip in Chelsea’s Champions League clash at the Mestalla and was carried off on a stretcher at half-time.

The 22-year-old insisted straight after the match that his injury was not as bad as he had first feared, but the Blues are still assessing their star striker.

Michy Batshuayi replaced Abraham off the bench in Valencia and will battle it out with Olivier Giroud to lead Chelsea’s line against West Ham this weekend.

Abraham has fired 10 goals and laid on two assists in a blistering Premier League start this term, but Lampard insisted he is confident the Blues boast the firepower to cope in his absence.

“The other lads have been training well, every day is a work day so whenever chances come they are ready and I have every confidence in them,” said Lampard.

“Michy has shown work ethic and quality, which I knew anyway. It’s not easy when you’re not playing as many minutes as you’d want.

“All my players want to play every minute of every game. With Tammy’s form that’s meant he’s played a lot of minutes, but that can obviously change now Tammy has his injury.

“I’ve seen a great work ethic and a persistence in how he works, and a consistency in his quality.

“We’ve seen when he has come off the bench at times as well. That has been great to see because we need competition in those places.”

Lampard will face the first game of his managerial career against former club West Ham, but insisted he remains unfazed by the occasion.

“I wouldn’t say it’s bittersweet in any way, it’s just a game for me; a game for us to try to win against a very difficult opponent,” said Lampard.

“It’s a London derby which adds spice to it, which the players have to be aware of. That can change the temperature of the game.

“I’ve played in games like this where teams turn up not in great form and are slightly transformed by the nature of the game. So we have to be very aware of that.

“I’m not concerned about the emotions of it from my point of view.

“I came through the academy there a long time ago, I’ve been at Chelsea a long time as a player and now as manager so my focus is completely on us.”

Brazil forward Willian this week revealed he believes the ball is in Chelsea’s court over a new Stamford Bridge contract.

The 31-year-old wants to extend his Blues deal and Lampard has confirmed he too wants Willian to stay.

“I said it before it is an ongoing situation with the club in terms of the contract and that is not so much by business,” said Lampard.

“You can see he is playing very regularly for us and playing well and I have said two or three times in the month that I am very happy with him, so you see where I am at with it.

“He’s a very important member of the club and of course I want it to be done but obviously both sides have to be happy for that.”