Raheem Sterling is set to be out for six to eight weeks with his groin injury but Manchester City and England team-mate Joe Hart's calf problem is only likely to sideline him for around a fortnight.
The pair picked up the injuries in Sunday's 1-0 Premier League derby defeat to Manchester United at the Etihad Stadium.
Speaking after the game, City boss Manuel Pellegrini suggested both players were facing up to a month out.
But, with scans having now been done, it is understood forward Sterling could be facing as much as twice that duration on the sidelines, while goalkeeper Hart could be back in a couple of weeks.
Joe Hart and Raheem Sterling are set to miss the upcoming England friendlies as Manchester City manager Manuel Pellegrini expects muscle injuries to keep them out for a month.
Roy Hodgson's men travel to world champions Germany next weekend for a mouth-watering friendly that is followed up days later by Holland arriving at Wembley.
However, the 24-man squad named on Thursday for those matches looks set to change after Sterling and Hart were injured as City lost 1-0 at home to rivals Manchester United on Sunday.
Sterling pulled up with a groin complaint midway through the first half and Hart was taken off on a stretcher after half-time, having sustained a calf injury trying to clear up a Martin Demichelis backpass.
"Both of them have muscle injuries," City boss Pellegrini said. "Raheem his groin and Joe in his calf.
"I don't think that a muscle injury you can be fit in one week. Normally three or four weeks."
Hart and Sterling join the likes of Wayne Rooney, Jack Wilshere and Luke Shaw on the sidelines.
Manchester City manager Manuel Pellegrini has backed winger Raheem Sterling to come good at Liverpool on Wednesday.
Sterling will be making his first return to Anfield since leaving the club for City in the summer. In the League Cup final on Sunday the England international was roundly booed by the Liverpool fans and is expecting more of the same this week.
I don't know which will be the starting XI on Wednesday but one player I am sure will start is Raheem Sterling.
He's a young player - he's starting his career - and knows how to deal with the pressure. He will maybe receive the same treatment when he arrives at Anfield but I'm absolutely sure he can play without any problem.
I don't have any doubt at all. It is important for him to play under pressure. I have 100 per cent trust in Raheem and I am sure he will be an important player in the game.
In the way he played the other day, he demonstrated that he worked for 95 minutes, always concentrating on the game. He missed a goal but that can happen to any player.
He was very difficult for (Nathaniel) Clyne in the one v one. I can understand after that game that he can play under pressure.
Raheem Sterling is confident Manchester City can go on and make a strong impact in the Champions League after progressing as group winners.
City claimed one of the top spots in the first stage of the competition for the first time as they came from behind to beat Borussia Monchengladbach 4-2 with two Sterling goals on Tuesday.
The result took them above Juventus to the top of Group D and means they will avoid the likes of Barcelona - their conquerors in the past two seasons - Real Madrid and Bayern Munich in the last 16.
Match-winner Sterling said: "It gives us massive belief. We all know this is a team that is going to score goals. We just have to be more solid on the whole and keep more teams at bay.
"I think it is just a matter of time and working on it as a team. Definitely it's paying off and hopefully we can carry that on to the next round.
"It was just trying to avoid probably some of the big guns in the next round and trying to get a good draw, as we know we can probably do it over two legs against most teams. We are just waiting for the draw now and will see who we get and take it from there."
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Raheem Sterling will hope to justify the fuss as Manchester City begin their at West Brom on Monday.
The England international will be the chief focus of attention at The Hawthorns following his acrimonious £49million move to City from Liverpool over the summer.
Much of the headlines surrounding the 20-year-old in recent months have been negative and he will want to make a quick start in City colours to turn discussion back to his football.
Manager Manuel Pellegrini is confident he can do that and has been pleased with how quickly the player has fitted in during pre-season.
"He has settled in very well. He wants to come here, he wants to have new challenges. I don't think he deserves criticism about that.
"He is working very well and it is easy for good players to settle in a good team. I think we are going to have a very successful player this year."
Raheem Sterling will emerge from the furore surrounding his transfer to Manchester City stronger for the experience, according to England boss Roy Hodgson.
The 20-year-old enraged Liverpool fans by making clear he wanted to leave Anfield after turning down a lucrative contract offer.
Hodgson believes Sterling coped mentally with any fall-out, and said:
He was playing for a club with a very strong fan base, not only in England but in other parts of the world, and unfortunately for him, I suppose, the fans locally at Liverpool took unkindly to the fact that he made it clear he wanted to move.
That is part and parcel of football really. I think if anything that will help him to mature and improve even more. I think for his age he is a remarkably strong and robust person, not just physically on the field but mentally.
And these things, if anything, will make him stronger. He has got a big price tag to carry around, but I think he is a good enough player to do so.