The Cleveland Browns will have some business to take care of soon, as center Alex Mack is expected to opt out of his contract. Mack signed a 5-year deal back in 2014, and it offered the option to opt out. There had been some chatter he might not opt out, but it is no surprise he will look to boost his salary coming off some strong work.
Ian Rapoport reported the expected opt out, but he is also reporting "a new contract is a real possibility." I'd imagine in most cases a new contract is a "real possibility", but that doesn't really clarify how close the two sides might be on a potential new deal. The belief is that Mack will wait until after March 1 to opt out because that means he avoids the franchise tag.
The San Francisco 49ers have plenty of questions about their offensive line, but I don't think they'll be investing heavy financial resources in the position. Daniel Kilgore returned in the middle of the year from his 2014 ankle injury, and looked solid. The only reason to replace Kilgore with Mack would be if the 49ers wanted to move Kilgore to right guard. Erik Pears, or maybe Anthony Davis are possibilities at the position.
Of course, Trent Baalke has not been one to spend big money on veteran interior linemen, so that is another reason the team might not be inclined to add Mack.