According to The New York Post, the vampire trilogy's studio, Summit Entertainment, has been unable to finalise promotional plans for Breaking Dawn's November release following the couple's personal troubles.
Pattinson and Stewart were alleged to have ended their relationship last month following revelations that Stewart had an affair with her Snow White and the Huntsman director Rupert Sanders.
"The studio's holding out to see if they get back together. But I don't think anyone is banking on that happening," a source told the publication.
"At this point, the press strategy would have been mapped out. It's usually very organised, but at this time it's undecided."
Summit has previously insisted that press for The Twilight Saga: Breaking Dawn - Part 2 is "full steam ahead" regardless of the stars' relationship status.
Pattinson and Stewart pulled out of convention appearances earlier this month, but are rumoured to be trying to repair their romance.
Watch a teaser trailer for The Twilight Saga: Breaking Dawn - Part 2 below: