BOSTON -- While the Mets are thrilled to have Jason Bay as their new left fielder, the star slugger -- if not for a medical dispute -- likely would have stayed with the Boston Red Sox.

In an interview with WEEI.com's Rob Bradford, Bay confirmed what MLB.com's Peter Gammons first reported earlier this week -- that the Red Sox and the outfielder had agreed in principle on a four-year, $60 million contract shortly after the All-Star break.

"That," Bay told WEEI.com, "is just one-tenth of the story."

The Red Sox had first broached a new contract with Bay during Spring Training of last year. The sides were too far apart at that time and agreed to table talks. Things again heated up in July, with Bay initially rejecting Boston's four-year, $60 million offer. The day after the All-Star break, Red Sox general manager Theo Epstein and Bay both publicly said that there would be no deal for the time being.

But unbeknownst to the public, Bay changed his mind a few days later and informed the Red Sox that he would accept their offer. This is where things got sticky.

Joe Urbon, Bay's agent, came to Boston to accompany his client for what seemed a formality -- a physical -- and also a news conference to announce the deal.

But as both Gammons and WEEI.com reported, after the physical, the Red Sox raised some red flags over the condition of Bay's knees and shoulder. The deal would have to be re-worked, the Red Sox told Bay. In Boston's new proposal, the first two years would be guaranteed at the same average annual value ($15 million per year), but the third and fourth year would be contingent on health and productivity. The Red Sox also wanted Bay to agree to have minor knee surgery after the 2009 season.

Things fell apart from there, particularly when Bay got a second opinion that didn't agree that his knees or shoulder were threatening his long-term health.

"I was shocked, to say the least, that I was being told to have knee surgery in order to get the contract," Bay told WEEI.com, "particularly since I wasn't hurt."

Bay and Urbon told the Red Sox about their second opinion after the season, at which point the sides revisited talks. At that point, the sides agreed to get a third opinion. That physician, according to WEEI.com, certified a letter saying that Bay "has an excellent future" and projected that he would "be able to continue to play at a high level at his position."

On the first night of the Winter Meetings, the Red Sox put three guaranteed years back on the table but wanted injury protection in the fourth year, similar to the contract they signed with J.D. Drew in Dec. 2006. Under such an agreement, if Bay had any injury problems with the pre-existing conditions that the club identified, the fourth year could be voided. The Red Sox also asked Bay to pay a significant amount of the insurance policy that would have gone with the contract.

None of that sat well with Urbon or Bay.

"Listen, I could understand the club wanting all these medical contingencies if I had spent any recent time on the DL," Bay told WEEI.com. "But I had no history of being a risk for injuries and I wasn't hurt."

On Dec. 12, Epstein told Urbon that the time had come to either accept or reject Boston's proposal. Urbon told the Red Sox that Bay had better offers elsewhere and later that day, the agent told several media outlets -- including MLB.com -- that it was unlikely his client would re-sign in Boston.

The Red Sox swiftly re-allocated the money they had earmarked for Bay, signing John Lackey to a five-year deal and also getting free-agent outfielder Mike Cameron.

Bay, meanwhile, found a home with the Mets, who also raised no red flags when putting him through a physical in early January. The Mets gave Bay a four-year deal worth $66 million with a fifth-year option that could bring the total to $80 million. The Mets didn't put any injury protection language in their contract with Bay.

"Much like the path of my career, this experience has not been a straight line, but it all ended up working out for the best," Bay told WEEI.com. "I have no regrets."