Marouane Fellaini could be on the sidelines until January, according to reports Getty

Manchester United could be forced to keep Marouane Fellaini at Old Trafford until at least January after the Belgian reportedly picked up a foot injury.

Fellaini had seemingly been certain to leave United this summer as Louis van Gaal looked to build a squad capable of qualifying for the Champions League.

Napoli had been edging closer to taking the 26-year-old on a season-long loan after discussions hit a stumbling block over compensation.

But the move has been thrown into doubt after the Express reported Fellaini had injured his foot in training and was spotted heading to hospital on crutches.

It means Napoli would likely back out of a deal to take Fellaini to the Stadio San Paolo and would have to wait until at least January, when the transfer window re-opens, to land him.

United have not confirmed the injury but could face a race to assess Fellaini before 1 September, the date the transfer window closes.

He was named as a substitute in the 2-1 defeat to Swansea City on Saturday, coming on as a second-half replacement for £29m summer signing Ander Herrera.

Reports from Italy said Fellaini would make a decison over a move to Napoli after the Naples club's Champions League qualifer against Athletic Bilbao on Tuesday.

Rafael Benitez's side drew the game 1-1, leaving them an uphill battle to make it through to the Champions League proper.

In other United news, midfielder Nick Powell is expected to go on loan for another season.

Powell spent last season at Championship side Wigan, scoring seven goals in 32 games from an advanced attacking role.

The 20-year-old joined United from Crewe Alexandra in 2012 for a reported £6m fee and has so far made two appearances for the Old Trafford club, scoring one goal.