Chargers reinforcements might not be on the way after all ... Derwin James tells TMZ Sports he's not sure yet if he'll be able to return from a foot injury this season.
"I don't know, man," the stud safety says. "I just got to keep healing and we'll see what happens."
Derwin -- who's one of the game's brightest young defensive players -- has been out since the summer after he needed surgery to fix a foot he busted up back at Florida State.
The 23-year-old was put on injured reserve and was expected to make a return sometime this season ... but now, he doesn't seem entirely sure that's going to happen.
In fact, when our camera guy asked if Derwin would be able available for either game against the Chiefs this year (one is Nov. 18, the other is Dec. 29), he said, "You gotta see. Tune in."
It ain't like James has suffered a setback or anything ... in fact, when he was out promoting phone company ROKiT in L.A. on Tuesday, he showed no signs of a limp and was having a blast.
It just seems like the dude's trying to get back to 100% ... telling us, "Feeling good, getting better, man. Getting healthy. Trying to get back out there."
We also spoke with James about the new NCAA rule that will help athletes get paid -- and ya gotta hear how he's is hoping that might lead to a new check for him soon!