Pace, 35, played Ronan the Accuser in the 2014 superhero film, reported Entertainment Weekly.
Gunn shared the news in a Facebook Q&A.
"Who knows," Gunn replied to a question about whether Ronan would ever show up again. "But not in 2, no," he said.
Gunn left, however, the door open for Pace's return to the franchise.
When asked in another segment of his Q&A whether he would ever consider having Pace return to the franchise, the director replied, "Perhaps someday."