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Media reports began circulating on Wednesday suggesting Morocco international Ziyech was a doubt for Monday's trip to Brighton and Hove Albion for the Blues' Premier League opener.

Ziyech arrived from Ajax in pre-season after a £33.3million deal had been agreed last term, with the forward boosting his reputation in 2018-2019 after a number of impressive performances en route to the Champions League semi-finals.

But Chelsea fans will have to wait a bit longer to see him in competitive action, as Lampard confirmed the reports he has sustained an injury.

Ziyech's fellow new signings Thiago Silva and Ben Chilwell are also not yet ready for their debuts.

"Ziyech took an injury to his knee in the friendly against Brighton and he won't be fit," Lampard said in Thursday's pre-match news conference.

"We are working on him and hope it will only be a matter of weeks, a couple of weeks, we hope, but we'll have to wait and see on that.

"Chilwell is working towards fitness. He won't be fit for Brighton. He has developed and improved this week and going in the right direction, which is good news for us.

"Thiago Silva is in London but won't be training until the weekend, so I doubt very much that he's in contention for the Brighton game.

"Out of the new ones, that's where we are at. Billy Gilmour is a longer-term injury, but other than that we are in decent shape."

Regarding Cesar Azpilicueta and Christian Pulisic, who were both forced off in the FA Cup final defeat to Arsenal in August, Lampard added: "I missed them off earlier – yes, I am certainly very happy to have them both back.

"Yesterday [Wednesday] was their first day fully training with the team, so they're in contention for Monday.

"I have to be careful and I have a squad to pick from, but the way they're training and their attitude to come back, it looks like they are over their injuries. I just have to make sure I manage them both back in their own ways."