Speaking at the Television Critics Association (TCA) winter press tour in Los Angeles, Reilly revealed that the sci-fi drama is losing money for Fox.
"He could not have been more clear," Jackson told Entertainment Weekly. "He's not running a charitable foundation. And if the show is really not making money [then that should be it]."
The actor, who plays Peter Bishop, added: "The important thing to me is that our writers are given a chance to finish the show [properly] because it's a serialised show."
Reilly himself also clarified his comments, insisting that Fringe will conclude in a satisfactory manner if its fourth season proves to be its last.
"I don't want it to go out with a whimper," he said. "We don't want to fumble the ball at the five-yard line. If it ends up being the last show, we'll end up doing it right."
Fringe returns to Fox on Friday, January 13 at 9/8c.
> Fringe future uncertain, says Warner Bros exec
Watch a promo for the return of Fringe below: