From MLB.com

"An MRI on the jammed left thumb of D-backs outfielder Justin Upton on Tuesday afternoon showed a bone bruise, and the All-Star is unsure if the injury will land him on the 15-day disabled list." Upton jammed his thumb while sliding into second base to break up a double play in the seventh inning against the Giants on April 8 and has not been the same since. He went 2-for-6 with a double, two walks, and two runs scored before jamming his thumb, and he's gone 5-for-24 since. "It doesn't seem like [Upton] will be 15 days, but it's not going to be tomorrow either," D-backs manager Kirk Gibson said. "We're are going to have to play short, and some guys are going to have to step up."

Stay tuned for more details, you may want to bench him in your fantasy leagues for now.