"It's about patience," Blues assistant boss Zola said.

"I know Bayern is very interested in him, but we're interested in him as well. We've proposed with him a contract for quite a while, so we're waiting to see what the player thinks about that.

"We certainly value him as a player. I know he hasn't played probably as much as he wanted, but this is down to the quality of the players in front of him.

"I've already told the player: it's not a waste of time. It's a time in which you can really get better, because you are pushed to do more.

"I hope Callum is using this time in a wise way. Right now, for him it's important to get better and better every day.

"He doesn't have to be focused on 'why didn't I play? I should be playing 20 games'. It's important: 'what should I do to be better than Willian, than Pedro, than Hazard?' and focus every day working on that.

"If he does that with the qualities he's got I've no doubt he's going to be a fantastic player. Hopefully he'll sign a contract with us."

Maurizio Sarri is poised to rotate his options against Forest after a busy period and with Tuesday's Carabao Cup semi-final first leg with Tottenham in mind.

Sarri is likely to rest Eden Hazard, at least as far as the substitutes' bench, with Pedro (hamstring) and Olivier Giroud (ankle) out again, but likely to be back in contention to face Spurs.

There are rumours the game could be Cesc Fabregas' last for Chelsea.

The midfield playmaker came on for his 500th appearance in English football on Wednesday against Southampton and afterwards applauded supporters.

His contract expires at the end of the season and he has been linked with a January move to Monaco or AC Milan.

Zola could not shed any light on Fabregas' future, saying: "I don't know how it's going to go."

Zola is uncertain whether Willian (hamstring) will be available to play at Wembley, but he will miss the Forest clash when Chelsea will seek to extend their 21-year run of reaching the fourth round.

That is the active record, but Forest beat then holders Arsenal 12 months ago to end the Gunners' 22-year run of advancing from the third round.

Zola added: "They have some good players in the team and the type of players that can cause problems. We will have to have a good day."

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