In 2007, Jon ruptured a tendon on that very foot, and missed the rest of the season. It's just over a year ago when something went "pop" in Lieber's right foot, and an aggravation of that injury is not out of the question. That's pure speculation, as I'm yet to find any details on Jon's status.
Micah should stick with the club until Soriano comes back, which should be soon. Derrek Lee isn't likely to need any rest at the moment, so the Cubs now have two immobile lefty hitters on the bench. Hmmm. Not sure I get that, but Hoffpauir is worthy of some at bats.