Saunders said he has struggled with the problem all season and had hoped he could work through it. He had started the season 5-1 but has gone 4-6 since then.
And after he lasted only 1 2/3 innings Friday night against the Texas Rangers, in which he gave up five runs, the Angels decided to put him on the disabled list.
The move should "let him get this little tightness out and then get back on the mound throwing and get back in the rotation, hopefully in a couple of weeks," Manager Mike Scioscia said.
His replacement in the starting rotation probably won't be announced until Monday or Tuesday, Scioscia said.
"I've got every confidence in the world that it's going to be fine," Saunders said. "It's pretty much just a knot in one of my big muscles back there and it's not going away."
Scioscia said, "I think Joe's crossed the line to where now it has affected his performance enough to where it's time to shut it down and hopefully regroup, take a half step back and take two steps forward.
"He's been trying to pitch with it for a while and at times he's thrown the ball well, but I think it's fairly obvious right now that he's a long way away from what he needs to be."
Rangers slugger Josh Hamilton, who overcame a widely publicized four-year struggle with drug and alcohol addiction, apologized Saturday after confirming that photos posted on the Internet showed him partying with three women at a Tempe, Ariz., bar in January.
Hamilton, who has three daughters with his wife, Katie, said "obviously she's disappointed and . . . I'm very embarrassed for her, the organization, for my children."
The 28-year-old right fielder said he told the Rangers about the incident the next day. Jon Daniels, the club's general manager, said that no disciplinary action was planned. "The first thing I did was apologize to them, because they trusted me and had faith in me and I let them down at that point," Hamilton told reporters in the Texas clubhouse at Angel Stadium as several of his teammates looked on. "They accepted my apology."
Hamilton and Daniels also noted that Hamilton is tested three times a week for substances banned by Major League Baseball. Hamilton played Saturday against the Angels.
Daniels said "my first reaction in January was concern, here's a guy who's obviously dealt with substance abuse at a pretty significant level."
But he said it was a positive sign that "immediately he came forward and was honest."
"He was remorseful, he was accountable," Daniels said. "It was not a good situation, not one that we wanted to hear about, but I do think he handled it as best as he possibly could have. All we can do is support him the best we can."
Asked about the details of the incident, Hamilton said "the details don't really matter, what kind of drink it was, it was just something that put me in a bad situation."
Angels baserunners had advanced from first base to third base on a single 89 times through Friday, tops in the big leagues. . . . The team also had a major league-high .305 batting average with runners in scoring position.
When: 12:30 p.m.
Where: Angel Stadium.
On the air: TV: Channel 13; Radio: 830, 1330.
Update: Lackey tries to extend his recent strong performance as the Angels close their three-game series with the Rangers. Lackey is 4-0 in his last five starts with an earned-run average of 1.86. He is 10-11 all-time against Texas. Holland is a 22-year-old left-hander who will be making his first start against the Angels. He lost his most recent start Tuesday in the Rangers' 6-0 loss to the Oakland Athletics.
-- Jim Peltz