Allegri revealed the news ahead of Sunday's game with Sampdoria.
He said, "Szczesny has a knee problem and will have keyhole surgery over the next few weeks, but he is available for tomorrow. Cristiano Ronaldo is not making the trip, as he needs to rest and has international duty coming up with Portugal. It's right for others to play now.
“Miralem Pjanic is coming, Blaise Matuidi and Federico Bernardeschi are suspended, Mario Mandzukic wanted to make himself more handsome and got a new nose (after surgery for a fracture), Alex Sandro had a muscular issue. You'll see Douglas Costa next year."