The England midfielder sustained the injury in a training-ground fall and is likely to be out for 'a few months' according to his manager Paul Lambert.

Delph is out of contract at the end of the season and has been a key player for Villa this season.

"Delph has had his operation, it went well and everything is on course," said Lambert. "It's just a matter of getting him to do his rehab and getting him fit.

"I don't think you can put a timescale on it but he will be out for a few months. It's not a complicated injury, it's straightforward.

"Everything went fine and it is now a case of getting him back."

Villa travel to QPR on Monday without Delph, whose place in central midfield could go to summer signing Joe Cole.

He has played just nine minutes in the Barclays Premier League for the club since joining on a two-year deal after leaving West Ham in July.

Thigh and hip injuries have stalled his Villa career but Lambert believes the 32-year-old could be key against his old West Ham mentor, now QPR boss, Harry Redknapp.

"Obviously Harry will know him really well but I have a good player on my hands - someone who can unlock a door," he said.

"He's been as good as gold. We try and play at high tempo, high intensity.

He's an excellent professional and has stayed behind after training, he's been really good.

"He had a thigh problem and that kept him out, then his hip. But the last few weeks he's been good.

"The number 10 role is Joe's strongest and that's where I see him. Systems are there to be adapted anyway, you can never really say you will play one way for the rest of the season anyway.

"I don't think Joe is too far away from starting, we will have to decide in the next couple of days. It will be a hard game and physical."