It was first reported on the Tacoma News Tribune web site.
Beltre disclosed after Saturday night's game against the Dodgers that he would have surgery on Tuesday in Los Angeles and it will be performed by Dr. Lewis Yocum. He also said that he might play in Sunday's series finale, although that remains up in the air.
"I don't think I can help the team like I wanted to, every day on the field," Beltre said of his decision to have the surgery sooner rather than later. "It got to the point it's really painful. My contribution won't be enough to help the team win. Hopefully I can get it fixed and come back 100 percent."
Beltre is expected to be sidelined for six to eight weeks.
"He feels very bad about it," general manager Jack Zduriencik said. "He likes what's going on here and wants to be part of this thing."
The Mariners go into Sunday's game three games behind the Angels in the AL West and 2 1/2 behind the Rangers.
Beltre had said as late as Friday night that the pain was getting worse and he was contemplating another surgery identical to the one he had last September in Seattle.
"I didn't know I would have [bone spurs] back," Beltre said. "They told me that 10 to 15 percent of the people who have the surgery have the spurs grow back again.
"I' m so lucky to be one of those guys," he added, sarcastically.
Beltre described the pain as "like being stabbed" and the only reason he hadn't shut it down sooner was because of the way the Mariners have been playing.
"If we were out of it, I probably wouldn't be thinking about [playing]," he said. "We're playing good, and I want to be part of something that might be special. We might get to the playoffs. Who knows?"
Beltre went into Saturday night's game batting .260 with five home runs and 30 RBIs, not nearly the kind of production he wanted during the final year of the five-year contract he signed prior to the 2005 season.
But his determination has been off the chart.
"He's a tough guy," manager Don Wakamatsu said. "By reputation, I knew coming in here that it was awfully hard to get him out of the lineup, no matter what. I know he has played off and on with his shoulder and it has gotten worse."
The pain has gotten progressively worse and he even has been removed for a pinch-hitter.
"When I raise my arm this high [shoulder high] it's there," Beltre said of the pain. "If I raise my arm over my head, it's there. If my swing raises my arm, it's there. Every time I dive for a ball, the pain is there. I want to keep playing. I'm going to keep playing and see what happens."
The shoulder ailment not only impacts the Mariners on the field, but puts management in something of a quandary. If, for some reason, the organization decides to make some personnel moves prior to the July 31 non-waiver trading deadline, Beltre would figure to be one of the players made available on the trade market.
But that might not be an option.
After undergoing two surgeries on the same day last September, one to repair a torn tendon in his left thumb and the other to remove the bone spurs from his left shoulder, Beltre was looking forward to a healthy season this year.
He reported to Spring Training ready to go, but deep down "knew I was never 100 percent," he said. "It was a gradual thing, and it kept getting worse. I was trying not to think about it, but in the last three weeks it has really gotten my attention."
The past two weeks have been physically brutal for the Mariners. They lost outfielder Endy Chavez to a season-ending knee surgery, and shortstop Yuniesky Betancourt suffered a strained hamstring early this week and went on the 15-day disabled list.
"It creates a dilemma, no question about it," Zduriencik said of the latest setback. "We have lost some vital part of our club, but it opens opportunities for other players. Guys have stepped up."
The short-term solution could be either Jose Lopez or Chris Woodward playing third base and someone, perhaps Mike Morse, being promoted from Triple-A Tacoma.
Minor League third baseman Matt Tuiasosopo, the perceived heir-apparent to Beltre, underwent surgery to remove bone chips from his right elbow and currently is on a rehab assignment in Arizona. He has played in only eight games this season.