The 20-year-old, who signed in the summer for £6 million but has yet to establish himself in the first team, had to be taken off the training pitch at Aston Villa's Bodymoor Heath complex on a stretcher, and immediately taken to hospital.
Should early fears that he has suffered a cruciate knee ligament injury be realised, Delph will be out for around a year.
A statement issued on the club's website last night read: 'Fabian Delph is awaiting results from scans taken to determine the extent of a serious knee injury he suffered in training on Saturday.
"The 20-year-old midfield player had to be stretchered off and immediately underwent tests. Doctors will know what damage has been done in the next 24 to 48 hours.'
Villa have turned down the opportunity to discuss the matter further, but Delph has in the past been criticised by Martin O'Neill for his, shall we say, excessive commitment in training.
'At this minute he hasn't really learned the art of tackling properly so he often leaves himself open to being injured,' O'Neill said in February.
'I don't want to knock any aggression out of him because that is part of his make-up. But he doesn't need to be going in in a manner that is almost dangerous to himself.
"He can learn, because his body is open up to injury and the slightest awkward turn and twist could mean he will do himself some damage.'