The Boston Red Sox have agreed to a deal in principle to acquire slugging first baseman Adrian Gonzalez, sources told ESPN The Magazine's Buster Olney on Saturday morning.

The Red Sox have received permission from Major League Baseball to negotiate with Gonzalez on a new contract, the sources said.

The team flew in Gonzalez, who had surgery Oct. 20 on his right, non-throwing shoulder to clean up the labrum, for a physical examination Saturday. While there was no official word on the physical, a team source told ESPNBoston.com's Joe McDonald that Gonzalez "looked good."

The Red Sox continued Saturday night to work on a long-term contract with him, a source, who indicated that the negotiation window will close at 2 p.m. ET on Sunday, told ESPNBoston.com's Gordon Edes.

Sunday's deadline came and went with no new information on the deal.

"There is not a contract agreement," John Boggs, Gonzalez's agent, said Sunday afternoon, as quoted in the San Diego Tribune. "I'm right in the middle of a meeting right now, I'll get back to you. We're still working."

In exchange, the Padres would receive three prospects in pitcher Casey Kelly, first baseman Anthony Rizzo and outfielder Reymond Fuentes, according to a baseball source. The Padres also would receive a player to be named later, a source told Edes.

"He's at the peak and prime of his career, which is going to be great," said Padres first-base coach Dave Roberts, a former Red Sox player and teammate of Gonzalez in San Diego. "I've talked to him numerous times about my experience in Boston, and I knew if this opportunity did present itself, he would be very excited to be a Red Sox. I think a lot of him as a player and as a person. Boston is going to be an amazing experience for him."