The Guardian report that Manchester United are concerned that Ander Herrera's injury could be more severe than first feared.
The Spaniard had to be withdrawn in the closing stages of their weekend match against West Ham United with a back injury, but originally the club were confident of a swift return to action.
They had planned to make an announcement about a minor injury on the official website on Monday, but concerns are growing that he could be kept out for a lengthy period of time now and the statement has been delayed.
It leaves Louis Van Gaal in an awkward scenario of not knowing whether to plan to have one his star midfielders back for the weekend's match against Everton or not.
If United are without Herrera, they are blessed with far more cover than they were in the early stages of the season, thanks to their sensational transfer window dealings, but Van Gaal will still not want to be without he Spaniard for too long a period of time.
Herrera has adapted to English football with consummate ease since completing a transfer from Athletic Bilbao last summer and United look a far stronger team with him in their side than without him.
His energy has meant that he has been a valuable outlet going forward, whilst he has also proven capable of getting in amongst opposition attackers.
United's attacking talents have stolen the headlines, but it is arguably Herrera that has made the best start to his Old Trafford career of all the new signings and he will be hoping that this latest injury set-back does not hamper his progress too badly.