Rooney sent for scans
Rooney limped off at club training and was sent to hospital for scans, which could cast a shadow over his availability for the FIFA World Cup in Brazil.
It is not Rooney's first injury issue nearing a World Cup, with his latest issue digging up memories of a broken metatarsal that stunted his involvement in Germany eight years ago.
It remains unclear if the injury is related to a chipped bone in his foot that required him to take pain-killing injections before the UEFA Champions League defeat to Bayern Munich at Allianz Arena three weeks ago.
With United languishing in seventh position in the Premier League, interim manager Ryan Giggs will be unlikely to risk Rooney should there be any doubts about his fitness heading into Saturday's home clash against Sunderland.
But England coach Roy Hodgson will be facing an anxious wait to discover if his star man will be available for their Group D campaign against Uruguay, Costa Rica and Italy in Brazil.
There is a little over a month before England's opening clash with Italy, and they have already lost Theo Walcott, Kyle Walker and Jay Rodriguez to injury, while Andros Townsend is also out of contention due to an ankle problem.