SAN DIEGO -- All-Star Alex Rodriguez was put on the 15-day disabled list on Friday -- because of his right knee, not his head.

	Rodriguez

The Seattle Mariners decided to sit their shortstop after an MRI exam showed he has a grade 2 sprain of his medial collateral ligament. The move was retroactive to July 8, so he'll be eligible to be activated on July 23.

Rodriguez sustained a concussion on July 7 when he was hit in the head by the knee of Los Angeles Dodgers shortstop Alex Cora as he attempted to break up a double play. He twisted his right knee when he fell after the collision.

All along, the Mariners were more concerned about the extent of Rodriguez's knee injury than the concussion.

"It's a great decision," an upbeat Rodriguez said after hearing the results of the MRI. "I'm very excited with the news. Anytime you have a knee injury, there's always the chance it could be season-ending or career-ending. I'll sit another 6-to-7 days, and the time will fly by."

Actually, counting Friday night's game against the San Diego Padres, Rodriguez will miss nine more games before he can be activated. He also missed the last two games before the All-Star break, missed his start in the All-Star Game and sat out Thursday's series opener.

Rodriguez, who is hitting .345 with 24 homers and 78 RBIs, is still able to take batting practice and field ground balls, which he did both Thursday and Friday.

"I think I can play tonight or tomorrow," Rodriguez said. "But there's no sense. I had the luxury of having the three days off during the All-Star break, and after this, I'll be ready to go."

Rodriguez missed 32 games early last season with torn meniscus cartilage in his left knee that required arthroscopic surgery.

Manager Lou Piniella was glad this injury won't require surgery.

"It could've been worse, but it certainly could've been better," Piniella said. "But the important thing is we'll have Alex nice and healthy for the last 2½ months."

Besides losing Rodriguez, the Mariners -- who lead Oakland by three games in the AL West -- are also hamstrung offensively on this six-game interleague trip since the designated hitter isn't used in NL parks. Unless Edgar Martinez makes a spot start at first, the most the Mariners will see of the best DH in baseball is a pinch-hitting appearance each game, like in Thursday's 2-1, 10-inning loss to San Diego when he singled to extend his hitting streak to 13 games.

Martinez is hitting .357, with a major league-leading 87 RBIs.

"That's a double-whammy," Piniella said. "We'll just have to make do and hopefully our other guys will step up."

That didn't happen Thursday, when Rodriguez's replacement at shortstop, Carlos Guillen, committed an error in the 10th inning that allowed the winning run to score.