Chicago.Cubs.MLB.com

By Carrie Muskat / MLB.com

(Jose) Macias will miss up to four weeks with a torn meniscus in his left knee. (Jeff Gross/Getty Images)

Macias, 32, was to return to Chicago on Thursday to undergo arthroscopic surgery. His knee has been bothering him for a couple of weeks, Cubs manager Dusty Baker said.

"Nobody thought it was this bad," Baker said. "I played a whole year with it. Sometimes it hurts, sometimes it doesn't. It kind of messes with your head."

Macias is the third Cubs player who will not be ready for Opening Day because of an injury, joining pitchers Mark Prior (inflamed Achilles tendon) and Mike Remlinger (shoulder).

"Hopefully we can be whole by May 1 with everybody," Baker said. "That's why April is important for us to do the best we can. That could be a blessing for us down the stretch. Guys could be stronger, especially guys like Remlinger and Macias."

Baker uses his bench a lot so losing Macias is not a minor issue.

"He's a valuable guy," Cubs general manager Jim Hendry said of the switch-hitter who was acquired in December in a trade for minor league pitcher Wilton Chavez. "It's going to hurt."

Infielder Brendan Harris, who batted .280 at Double-A West Tenn. last year and .302 in the Arizona Fall League, would have been a leading candidate to substitute for Macias but Harris underwent surgery for a similar injury earlier this spring and isn't ready yet.

Replacing Macias isn't as simple as finding another body. Infielder Scott McClain leads the Cubs in home runs this spring but he is a non-roster invitee and the team would have to drop someone from the 40-man roster to make room.

"We've got roster problems," Baker said. "Everything's up in the air. It's a new twist."

The Cubs could carry 12 pitchers rather than add a backup infielder/outfielder, although that's not an option Baker wants to consider. What do the Cubs need the most?