The Uruguay striker started against Burnley at Turf Moor in midweek with our interim boss saying that he chose Cavani for the task in Lancashire because of his fighting qualities.
The 34-year-old was denied a goal when his header was saved by Nick Pope from close range.
Later, he was substituted in the 68th minute with Cristiano Ronaldo coming on in his place for the final push in the 1-1 draw.
Our interim boss has told MUTV that Cavani picked up a groin injury in training and was unfit to face the Saints today.
As a result, he has brought Ronaldo back into the starting XI as we look to get back to winning ways - the only change to those on duty in midweek.