The Pirates first baseman jammed the thumb on a play along the first-base line and was taken out before the 10th inning.
LaRoche, who was replaced by Doug Mientkiewicz at first on Sunday, is available to pinch hit, but manager John Russell is likely to hold LaRoche from the lineup until Pittsburgh begins second-half play on Thursday in Colorado.
The injury comes at a bad time for LaRoche, who has 18 hits in his past 40 at-bats (.450).
In other injury news, Phil Dumatrait played catch on Sunday morning from a distance of 45-60 feet for about five minutes, the left-hander said.
Although the pain continues in his left shoulder, Dumatrait said it's beginning to feel better every day.
Todd Krise is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.