Manchester City are sweating on the fitness of captain Vincent Kompany, with the Independent reporting that the defender will see a specialist about his hamstring injury.
Kompany, 26, limped off during the first half of City's 3-2 loss to rivals Manchester United at the Etihad on Sunday, with Kolo Toure replacing him.
It had been hoped the Belgian centre-back would make a swift return to full fitness, but there are now concerns over whether he will be available for this weekend's trip to Newcastle United.
City trail United by six points in the Premier League title race, and the availability of Kompany is key to their bid to defend the title.
Kompany signed for City from Hamburg for £6 million in 2008, and has since made 138 league starts for the club, enjoying a particularly impressive 2011-12 campaign and being named the Premier League Player of the Season.
Meanwhile, City defender Micah Richards has said he hopes to return to action by early February after undergoing knee surgery in October.
Richards, 24, tore the meniscus in his right knee but is gradually making progress in his rehabilitation.
"I am not putting a date on when I will be back because these things are never exact, but I am hoping it will be in early February,'' he told City's official wesbite.
"There is still not too much I can do, but I am now on one crutch instead of two, so that is progress.
"Of course it is frustrating and there is nothing more I would like than to be out there playing, but I am being well looked after, the injury is responding and the knee getting stronger every day."