The slick fielder was hurt diving for a ball during a game in New York against the Mets last week. An MRI and CAT scan Monday revealed not only a bruise but fluid in Arenado's lungs.
Rockies manager Walt Weiss said it's ''going to be a few days before he's even up and about. But I think we'll see him before the season is over.''
Arenado is hitting .287 with 18 homers and 61 RBIs.
Colorado recalled right-hander Eddie Butler from Double-A Tulsa on Tuesday. The prized prospect may start this weekend against Arizona.
Butler made one start earlier this season before going on the DL with an inflamed rotator cuff.