"The irritation has been building," Lieber said. "I probably could pitch, but this way it'll have more time for it to heal."
Lieber, 38, is 2-3 with a 3.43 ERA. He was placed on the 15-day DL retroactive to July 11.
"It's the same foot that he had the surgery on; he was limping around a little bit," Cubs general manager Jim Hendry said. "Seemed like he could probably go in five to seven days without much trouble, but we figured once you're going to miss that much, we needed to get another player up here.
"Jon is the consummate pro in that he probably didn't want to go out 15 [days], but understood that he was going to limp around for five to seven, so it wasn't a bad time."
Hoffpauir, 28, begins his third stint with the Cubs. He hit .400 (14-for-35) with six doubles, one RBI and eight runs scored in 18 games. He made his Major League debut May 18 against Pittsburgh and collected his first career hit on May 21 in Houston, going 2-for-4 with a pair of doubles and a run while starting in left field.
"I've got zero expectations as far as playing time," Hoffpauir said. "I'm here to help as much as I can, however I can."
Hoffpauir, a native of Fort Worth who resides in Jacksonville, Texas, was in uniform for Friday night's game against the Astros. A number of friends and family made the trip south to Houston.
"Quite a few," Hoffpauir said. "Most of my family is from about 2 1/2 hours from here. Tonight I've got a few, but Saturday and Sunday I'll have a pretty full pass list."
Originally selected by Chicago in the 13th round of the 2002 First-Year Player Draft, Hoffpauir has appeared in four games at first base and three games in left field. As a pinch-hitter, he has gone 2-for-7 (.286) with an RBI and a walk.
"Right now I really just have to learn to become more of a selective hitter," Hoffpauir said. "Hit the good pitches and take the bad pitches and the borderline pitches, and take my walks when it's that time."
In 36 games with the Iowa Cubs, Hoffpauir batted .358 with 11 homers and 52 RBIs after missing the first month of the season with a strained left oblique.
The Cubs hope to get reliever Scott Eyre back from the disabled list soon. Eyre threw a bullpen session on Thursday.
"Scotty's champing at the bit to come back," Hendry said. "He won't be active tonight or tomorrow. We'll play it by ear after that."
Jim Molony is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.