SEATTLE -- A frustrated Carlos Silva stood in front of his locker inside the Mariners' clubhouse at Safeco Field on Sunday with a menacing look on his face.

He was not happy and sparred with some of the media asking questions.

The veteran right-hander later apologized for his demeanor, blaming his mood on the continuing problems incurred during a season that has not gone nearly like he, or the Mariners, expected.

His latest disappointment occurred in the fourth inning Sunday afternoon, when tightness in his lower back brought an abrupt halt to his 21st start of the season.

The last pitch he threw was sent into the left-field seats for a three-run home run, putting the Indians ahead to stay in their eventual 6-2 victory.

"Right now, the news is pretty good," interim manager Jim Riggleman said after the game. "The training staff and doctor checked him and didn't see anything. There was a little spasm -- or something -- there, and hopefully it won't cause him to miss a start. We'll know more in next day or two, but we think he will be all right."

Silva said he wasn't sure about his status for his next scheduled start, next Saturday in Toronto, and advised the media to ask the team trainers.

Riggleman said he first noticed that Silva might have a health issue during the fourth inning. The first batter doubled and the second one reached on an infield single. The next -- and final -- pitch Silva threw was hit by Kelly Shoppach for a home run.

"The pitch before that showed something," Riggleman said. "Kenji [Johjima] went out and checked on him, and Carlos said he was OK. After the home run, we went out, and he didn't protest too much about coming out."

The Mariners signed Silva to a four-year, $48 million contract during the offseason. He came out of Sunday's start with a 4-12 record and 5.62 ERA.