Pirlo left the Rossoneri after a decade this summer when he joined rivals Juventus on a free transfer.
"We already miss Pirlo," Abbiati said. "He's a great champion and I wish him all of the very best.
"We played together for many years, also for the Under-21 side, and he's a great friend. Juventus made a great signing."
Abbiati played a key role in the club's Scudetto success last term, but he concedes another Italian championship may be tough.
"All of the clubs have strengthened and we'll all start from the same line. Napoli are the side who have improved the most so far."