McCutchen, 27, suffered the injury roughly two weeks ago, soon after being hit by a pitch in a game against the Diamondbacks. The beaning was in retaliation for a pitch earlier in the series that hit Paul Goldschmidt, breaking his hand and ending his season.
In 109 games before getting hurt, McCutchen was hitting .311/.411/.536 (166 OPS+) with 32 doubles, 17 home runs and 17 stolen bases. He has actually improved on last year's NL MVP-winning performance.
The Pirates come into Tuesday having lost six straight games. They are 64-61 overall, putting them six games back in the NL Central and two games back of a wild-card spot.
To make room on the roster for McCutchen, the Pirates sent utility man Michael Martinez to Triple-A.