Santon left AS Roma this summer after his contract with Jose Mourinho's side expired, having not made a single appearance in the 2021/2022 campaign due to fitness issues.
Santon came through the Inter Milan youth ranks and broke into the first team in the 2008/2009 season, helping the Nerazurri win the Serie A that campaign and a famous treble under Mourinho the following season.
Santon spent three-and-a-half seasons in England with Newcastle United before returning to Inter in 2015.
He joined Roma in 2018 as part of the deal that took Radja Nainggolan to Inter and remained at the Stadio Olympico until this summer.
"I'm forced to stop playing," Santon told Tuttomercato.
"Not for not having had offers, not for anything else, but because my body, with so many injuries in the past, can't take it anymore.
"I didn't want to do this, but I have to. I had endless tests and consultations, but there was nothing to be done. I can still walk, but that's not enough to be a professional athlete.
"If I kept pushing, I'd risk needing a prosthesis. The left knee is just gone. It stops me doing lots of things.
"The right knee, that had surgery three times, removing cartilage, the entire external meniscus, so as soon as I strain it even a little bit, it swells up and can't bend.
"All my injuries really came from there, because if the right knee can't bend, you put more strain on the left and the flexor. If you play one match, you risk being out of action for the next five."
Santon won eight caps for the Italy national team.
