The Saints placed Watt on the Reserve/Retired list Wednesday, Josh Katzenstein of The Times-Picayune reports.
Watt was waived by the Chargers, who took him in the third-round of the 2014 draft, halfway through last season. He ultimately missed the entire year with a knee injury before signing a contract with the Saints in June. His retirement, at least the timing of it, definitely comes as a surprise.