The 36-year-old penned a new one-year contract last summer.
"It's clear that you start to pick up a few injuries as you get closer to your 37th birthday," the goalkeeper said.
"However, I remain at the club's disposal for anything. There is no law saying that I have to be the first choice forever.
"But it is clear that when Milan say stop, then I'll say stop. If I don't sign a renewal then I will probably quit the game."
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