The Argentina right-back felt severe pain in his hamstring during Tuesday's game against Leicester City and the club are concerned that he could be out until the middle of January
Manchester City fear Pablo Zabaleta could be out for a month with a hamstring injury.
The Argentina international limped out of Tuesday night's Capital One Cup win over Leicester City, and the club are holding out hope the player suffered a spasm, rather than a tear.
The club's medical staff are not optimistic, however, and expect scans to indicate a serious injury which could rule him out for as many as seven matches over the next four weeks.
City are prepared to deploy James Milner at right-back over the festive period, given Micah Richards has also been ruled out with a hamstring injury picked up against Bayern Munich last week.
Milner has found form in midfield in recent weeks, particularly in the 3-2 win at the Allianz Arena, but has played at right-back at former club Aston Villa.
Meanwhile, Stevan Jovetic is set to make his return to the City line-up against Fulham at the weekened after missing Tuesday's 3-1 win through illness.
The Montenegro striker picked up a calf injury against Newcastle at the end of October but had resumed full training in recent weeks and was expected to make his comeback against the Foxes.