SAN FRANCISCO -- Cubs reliever John Grabow's season has ended.

Grabow felt something pop in his left knee during a rehab outing Monday in Mesa, Ariz., and an MRI on Tuesday revealed a Grade 3 sprain. He will have his knee immobilized for four to six weeks and be examined by the Cubs' orthopedic specialist to determine the next step.

Grabow has been on the disabled list since June 29. He appeared in 28 games and had a 7.36 ERA.

Aramis scratched with sore rib cage

SAN FRANCISCO -- Cubs third baseman Aramis Ramirez was scratched from Wednesday's lineup because of a sore left rib cage. His status is day to day.

Cubs acting manager Alan Trammell said Ramirez apparently dove for a ball a few days ago and felt something in warmups Wednesday. Ramirez told Trammell he wasn't available after batting practice.

The Cubs already were one man short after trading infielder Mike Fontenot to the Giants about two hours before the game, which San Francisco won, 5-4.

Ramirez became the 266th player in Major League history to drive in 1,000 runs, doing so in the first inning Tuesday with a RBI single against the Giants' Tim Lincecum. Of the 1,000 RBIs, 684 have come with the Cubs, which ranks 15th in franchise history. Charlie Grimm is 14th with 696.

Ramirez was batting .228 in 86 games with 16 home runs and 54 RBIs. Jeff Baker started at third base Wednesday and was expected there Thursday as well.

Hoffpauir endorses Sandberg as manager

SAN FRANCISCO -- If Ryne Sandberg needs a reference as he pursues a big league managing job, he can call Micah Hoffpauir.

Hoffpauir, who has played for Sandberg this season at Triple-A Iowa, said the Hall of Fame second baseman supported him when he struggled during the first two months.

"I like him," Hoffpauir said. "I think he's a great players' manager; I think he knows the game. I don't see any reason why he wouldn't be a great big league manager.

"He loves to be in the locker room and if the pitchers are out throwing, he's out there talking, hanging out, seeing what they're doing," Hoffpauir said. "If we're in the cage, he comes in. He's always around, he's always there. I think he's going to be a good manager."

Hoffpauir, called up from Iowa on Tuesday to take Derrek Lee's spot on the roster as the first baseman deals with his ill grandfather, was batting just .188 in the first two months of the season. Sandberg stuck with him, said he was a leader on the team and kept playing him.

"That's the thing I appreciate from him," Hoffpauir said. "I think he's a good dude, a good man."

What happened at the start of the year?

"I let some stuff get the best of me and you can't let that happen," Hoffpauir said. "I got angry. Obviously, coming into spring, I thought I had a chance to make the team and I didn't. I was upset. I wasn't mad at the team, I was mad at myself. I didn't do what I was supposed to do in spring."

Hoffpauir was able to get into a routine and found his swing. He raised his average to .273 with 20 homers and 87 RBIs.

Sandberg has gotten lots of media attention since Lou Piniella announced he was retiring at the end of this season. The Cubs will be looking for a new manager and Sandberg has made it clear he'd like the job.

"I think Ryno's worried about one thing and that's getting himself ready to be in the big leagues," Hoffpauir said. "I was walking by the other day and a reporter asked him, 'Do you want to manage in the big leagues?' and he kind of giggled and said, 'Yeah, that's why I'm doing this.'

"He's there in Iowa trying to learn as quickly and as well as he can how to be a manager, how to handle a game," Hoffpauir said. "I think he's done a great job. He's shown maturity from the standpoint of being behind his players. That's one thing I absolutely love. He's very quiet and soft-spoken but if something happens, he's got your back."

Hoffpauir's status next year is in doubt, too. The first baseman, named the Pacific Coast League Player of the Week after batting .536 with four doubles, three homers and 12 RBIs in seven games from Aug. 2-8, doesn't know what's in store for 2011. Lee is a free agent after this season and not expected to be re-signed.

"If they give me the opportunity to fight for that position, I'd love it," Hoffpauir said. "I'd love to play in Chicago for the rest of my career. It's a great city, the fans are wonderful and it'd be great to win in Chicago."

Castillo makes Major League debut for Cubs

SAN FRANCISCO -- The Iowa Cubs players and staff were teasing Welington Castillo that it was his fault pitcher Marcos Mateo nearly missed his flight to join the big league team.

Mateo, called up Monday from the Triple-A team, was Castillo's roommate in Des Moines.

"I started to get a little angry about it," Castillo said of the joking. "I said, 'It's not my fault. He's a grown man.'"

Then, Iowa Cubs manager Ryne Sandberg started to laugh.

"He said, 'You're going to the show,'" Castillo said.

The rookie catcher was added Tuesday to take Geovany Soto's spot on the roster. Soto was placed on the 15-day disabled list retroactive to Saturday with a mild ligament sprain in his right shoulder.

Castillo made his Major League debut Wednesday night behind the plate and doubled in his first at-bat in the second inning against the Giants' Barry Zito. He's the second Cubs rookie to get a hit in his first at-bat this season, joining Starlin Castro, who homered in his first on May 7 against the Reds.

Castillo tried to get some sleep Tuesday after a long day of travel from Des Moines to San Francisco but had to deal with congratulatory calls from family and friends in the Dominican Republic.

On Wednesday, it was time to go to work.

"It's a little cold here," he said of San Francisco. "I came from Des Moines where it was really hot. I'm not going to think about it, I'm going to try to play well and do what I can to help the pitcher and try to win the game."