"Obviously, it's a tragic deal," Mullen said.
Franks, who started 23 games entering Saturday, suffered the injury during the third quarter with his team trailing by 11 points. The ankle was immediately placed in an inflatable cast and he was carted off the field, surrounded by his teammates.
"I went out there and I was with him, you know, told him we all love him, we're there for him, and he'll be all right," Mullen said. "I think the team [gathering around Franks] shows what he means to the team, and what the team thinks of him, you know as the leader of the team, and the type of guy he is, how hard he works, to go do that. And shows a lot about him and what the team thinks.
"It really, to me, shows the respect that they have for his leadership and the love that they have for him."
Franks was replaced by junior Kyle Trask, who completed his first four passes and ended the drive by pitching the ball to Lamical Perine, who ran 8 yards for a touchdown. Trask then ran in the go-ahead touchdown with 4:11 left in the game.
"Kyle was waiting for his moment," Mullen told ESPN. "The team believes in him and we believe he's a starter, just like Feleipe is. ... There was never a doubt he could do the job."
No. 9 Florida hosts Tennessee on Saturday.