Source: 49ers after Olin Kreutz

Negotiations continue between the Bears and free-agent center Olin Kreutz, but the San Francisco 49ers have emerged as a serious threat to end the Pro Bowler's 13-year run in Chicago.

An NFL source said that the Niners sent Kreutz a contract proposal Wednesday night. Although the Bears and the center have talked numbers as well, the source said that Chicago's offer doesn't reflect how important he is to the team. For a squad that allowed a team-high 56 sacks, Kreutz was seen as a constant as the Bears try to rebuild the rest of the offensive line.

Kreutz is expected to agree to terms Friday with one of the teams.

"It would hurt," Bears safety Chris Harris said Thursday on "The Waddle & Silvy Show" on ESPN 1000. "Olin is the team leader. He's that guy. He's been around the league for I think 13 seasons, he's very well respected, probably the most respected person in our locker room.

"Olin, he's a smart guy, he's very smart. You gotta be to play center, making all the checks. They are really a close group on the offensive line. It's like really cliché -- one for all and all for one, but that is our offensive line, and he is the leader of the offensive line. I really would hate to see him leave. I really want to see him back."

The Bears have been deliberate at the start of free agency. They had expressed interest in New York Jets free-agent wide receiver Brad Smith, but ESPN NFL Insider Adam Schefter reported Thursday that he will sign with the Bills.

So far, former Jaguars punter Adam Podlesh has been the club's only addition in unrestricted free agency. ESPNChicago.com also confirmed that the team is shopping tight end Greg Olsen.

Kreutz has declined more lucrative offers from other teams in the past to remain with the Bears. But this time could be different. Of all of the free-agent centers to come onto the market, Kreutz has been to the most Pro Bowls (6). In addition, he has started in a team-high 134 consecutive games, a streak he started in 2002.

Kreutz's experience and leadership ability already are valued in Chicago, but those attributes also are attractive for a 49ers team set to start the season with a new coach in former Bears quarterback Jim Harbaugh.

In addition, sources told ESPNNewYork.com that the New York Giants have agreed to a deal with last year's starting center for the Niners, David Baas.

Bears coach Lovie Smith, offensive coordinator Mike Martz, and offensive line coach Mike Tice each made it clear all offseason that the club wanted to bring back Kreutz to direct what will be an inexperienced offensive line.

Michael C. Wright covers the Bears for ESPNChicago.com and ESPN 1000.