The 24-year-old suffered a dislocated shoulder during training in October and Lambert says that the England international will endure several months of rehab before making it back into the first team.
The former Leeds United man is set to see his role in the middle of the park filled by former West Ham and Chelsea playmaker Joe Cole.
"Delph has had his operation, it went well and everything is on course," Lambert explained to the media. "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."
Cole, a former student of Harry Redknapp at West Ham in the late 90s and early 2000s, is set to go up against his old boss's QPR at Loftus Road on Monday.
Lambert says that, while the 32-year-old's fitness is not quite up to running out 90 minutes, he is happy to have the veteran fill the vacant No.10 role.
"Obviously Harry will know him really well but I have a good player on my hands - someone who can unlock a door," he enthused. "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 No.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.
"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."