Chelsea boss Antonio Conte says Eden Hazard and Tiemoue Bakayoko are both recovering well from injury.
The Belgium international broke his ankle while on international duty with Belgium with Bakayoko still recovering from a knee injury.
The two have missed pre-season and are expected to also miss the start of the season.
"It's difficult to say because when you arrive from a bad injury, after surgery, it's not easy to programme an exact date to come back," Conte told reporters.
"They are recovering very well and everybody knows the importance of these players for us.
"Every single player must be in the best form to play, otherwise we risk putting the player in a bad position and then to have damage for the team.
"Bakayoko doesn't know anything about my idea of football and he will need a bit of time to adapt and understand.
"This is the great difficulty for a coach who has an idea of football and wants to give the team an identity. It's the same now for Morata and Rudiger. If the player arrives as soon as possible it's easier for me."
