Despite expressing a desire to leave West Ham last year, Sakho remained at the London Stadium but the 28-year-old continues to be linked with a switch to another club.
However, Irvine has insisted that the striker's recent absence is down to injury, rather than manager David Moyes protecting him ahead of a departure elsewhere.
Irvine told reporters: "Absolutely. He is injured at the moment, has been since the window opened so he's not been on the training ground at all, I've seen very little of him to be honest.
"He is not available for selection, it's as simple as that."