MANCHESTER, United Kingdom - Manchester City manager Manuel Pellegrini admits it's impossible to know how long knee ligament injury victim Sergio Aguero will be sidelined after the star striker hobbled off in the 1-0 win over Everton.
The Argentina international, the Premier League's top scorer with 14 goals, limped out in the second minute when he jarred his knee as he stretched for the ball in a challenge with Muhamed Besic.
City's medical staff will assess Aguero on Sunday to determine the extent of the injury and how long they expect the 26-year-old to be on the sidelines.
Pellegrini has already ruled Aguero out Wednesday's decisive Champions League game against Roma in which City must better CSKA Moscow's result against Bayern Munich to progress to the knockout stage.
"It is not good news, I don't think he will be able to play," Pellegrini said.
"We must wait for the diagnostic, the important thing he will not play against Roma and that is a very important game. It's impossible to know how long he will be out.
"He has a problem with his ligament in his knee and on Sunday we will know better how serious it is.
"It's very difficult if you have trouble in your ligament to recover in a few days. Of course it's a big problem, because Sergio was in a very good moment and is an important player for our team." Premier League leaders Chelsea slipped to a 2-1 defeat to Newcastle United earlier in the day which meant City's victory moved to them within three points of the London club.
The victory over Everton came thanks to a Yaya Toure's 24th-minute penalty and Pellegrini said it proved his side are not just one-man team reliant on Aguero.
"Of course I always say this team is not just Sergio Aguero," Pellegrini added.
"The way we won was important for what we showed in defence. Sometimes it's important to just win 1-0.
"We had a chance to score another goal and didn't so I am pleased for the defence because they are criticised a lot, but I thought they did very well.
"It was important for a lot of things. Chelsea lost their game and it was important to recover the points and to be the near the leaders.
"December is a very different month where we have to play a lot of games. It's a month where maybe you don't win the title as such, but it is a key month to try to start the next year near the top." Everton boss Roberto Martinez criticised the decision by referee Andre Marriner to award City the match-winning penalty.
James Milner went down in the area following a slight nudge from Everton captain Phil Jagielka but Martinez felt the decision was a harsh one.
"It was a wrong decision," said the Spaniard. "When you see a ball come into the box, James Milner takes the ball away from the direction of Phil, there was contact but no contact of trying to make a foul.
"Football is a contact sport and for that to be a penalty is a big, big difference." Everton have now only won once in their last six Premier League games and remain seven points adrift of fourth-placed Manchester United.
But Martinez was satisfied with the response of his players in the second half against City.
"Our confidence left us after the penalty and we couldn't show what we are as a team. But I thought the performance after the break was good," Martinez added.