Joe Johnson says he's been living in the gym and staying in shape in case an NBA team comes calling ... telling TMZ Sports he'll be ready to go if a squad needs him for the playoffs.
38-year-old Iso Joe made a hyped return to the Association in October when the Detroit Pistons scooped him up from the BIG3 ... but got cut during training camp.
Joe tells us there's no hard feelings with how it went down in Motor City, saying his body wasn't right at the time.
"I was banged up with a lot of injuries, didn't get a chance to really rest," Joe tells us.