Chicago Cubs left fielder Alfonso Soriano is out indefinitely with a sore left knee.

Cubs manager Lou Piniella said Friday the team plans to hold Soriano out of the lineup for a while, giving him time to rest and treat his ailing knee. Piniella said at some point the club will "revisit" the situation, but he's not sure when.

"There's no timetable," Piniella said.

Asked whether Soriano could miss the rest of the season, Piniella said he wouldn't go that far. The Cubs were six games behind NL wild-card leader Colorado heading into Friday night's game against the New York Mets.

Piniella said he spoke with Soriano before the game and explained the situation.

"He's agreeable to that, yeah. I told him, I said, 'Sori, I mean, I really appreciate the fact that you're toughing this thing out and wanting to play and not complaining. But boy, I mean, it's hard enough when you're feeling full strength as opposed to when you're not,'" Piniella said.

Sam Fuld started in left field Friday night in place of Soriano.

"The crux of it is, his knee is not strong. He's having trouble playing on it, hitting on it," Piniella said. "You can't move, you can't push off without your legs."

Trying to play through the injury, Soriano has struggled on offense and defense. He missed a fly ball for an error Thursday during a 5-0 loss to the Chicago White Sox and was booed loudly by the Wrigley Field crowd when he struck out to end the game.

"This is the right approach," Piniella said. "I thought about this long and hard yesterday on the airplane trip from Chicago to here, and all last night I vacillated. This morning, I still felt the same way. This is the best thing to do for this young man and I stick to it."

Soriano had a cortisone injection in his knee Sunday and missed three games during the week. He said doctors told him he might need minor surgery after the season to clean out his knee, something he'd rather avoid because he's never had an operation, he said.

"If they're going to make my knee better, I have no choice," he said. "It's getting worse."

Soriano, who made seven straight All-Star games before missing out this year, is batting .241 with 20 homers and 55 RBIs. He has nine stolen bases and 11 errors, plus a paltry .303 on-base percentage.

Piniella said Soriano could be available to pinch hit, but he'd like to stay away from that for a while.

"For now, we're just going to rest him and give him a chance to get this thing stronger and hopefully he can come back and play the way he's fully capable of," the manager said.

Soriano, who has eight consecutive 20-homer seasons, is 10 for 61 (.164) with six RBIs in his last 17 games, though he did hit a decisive, three-run homer against the Mets last Friday at Wrigley Field to cap a 3-for-3 day at the plate.

In other news, first baseman Derrek Lee missed his second consecutive game to be with his wife, who gave birth to their second child early Thursday morning. Piniella said he expected Lee back on Saturday.

"I hope he remembers it's a day game," Piniella said, laughing.

Micah Hoffpauir started at first base against the Mets.

The Cubs also recalled infielder Bobby Scales from Triple-A Iowa and claimed right-hander Thomas Diamond off waivers from Texas.

Scales batted .241 with three homers and seven RBIs in two previous stints with Chicago this season, appearing in 25 games. He was available off the bench Friday night.

The 31-year-old Scales played in 1,013 minor league games before making his major league debut this year.

Diamond was assigned to Iowa. Selected 10th overall by the Rangers in the June 2004 draft, the 26-year-old pitcher was 2-3 with a 4.20 ERA and one save in 38 games with Double-A Frisco and Triple-A Oklahoma City this season. He missed the 2007 season following elbow ligament replacement surgery.