Mack was named to his third Pro Bowl on Tuesday, having come back from a fractured ankle and ligament damage that cost him 11 games in 2014.
Mack's strong finish overcame a slow start, sending him to Hawaii for the third time.
Because of a decision made when Mack was a free agent after the 2013 season, he can opt out of the final three years of his contract after this season.
Mack was coming off a Pro Bowl season in '13 when the Browns decided to give him the transition tag instead of the franchise tag. The transition tag saved the team about $1 million compared to the franchise tag, but it also allowed Mack to shop himself to other teams. (The franchise tag effectively keeps free agents with their teams.)
Mack signed an offer sheet with Jacksonville that the Browns quickly matched. But the deal gave Mack the right to be an unrestricted free after this season if he so chooses.
That means the Browns could lose their Pro Bowl center in addition to other free agents who also could hit the market, most notably safety Tashaun Gipson, tackle Mitchell Schwartz and receiver Travis Benjamin.
"It's in his favor that he has that in his contract," head coach Mike Pettine said of Mack. "We'll react accordingly. Alex Mack is a Cleveland Brown. We'd love to have him here and be a part of what we're doing. That's a decision that will be made down the road."
Mack has made good money under this deal. His base salary was $10 million in 2014, $8 million this season. He is to make $8 million annually over the final three years of the deal. The website overthecap.com reports that Mack's average per year of $8.4 million ranks fifth in the league among centers.
Mack has to decide two things:
Does he want to stay in Cleveland? And if he doesn't, can he earn the same kind of deal on the free-agent market?
If he does opt out, the Browns have another issue to solve. They drafted Cam Erving with their second pick in the first round in the spring, but Erving has struggled.
Mack's decision will ripple, and it will be one of the more important ones affecting the Browns this offseason.