Pirlo pulled up during Friday's training session with a calf strain.
"We will take the medical tests one day at a time and keep a constant monitor on his situation," explained Italy medical chief Enrico Castellacci.
"For this type of injury you generally expect to be out for 15-20 days, but it depends on the individual physique of the player.
"We think he could recover for a few games. It's up to the Coach to decide, as all we can do is give a medical opinion."