Schierholtz initially sustained the injury when he fouled a ball off his foot last Monday. He sat out the next day but was able to play through the pain until Sunday.
The left-handed hitter was in a walking boot Tuesday after an MRI revealed the fracture.
Schierholtz was one of two candidates to take Carlos Beltran's place on the 15-day disabled list. Pitcher Jonathan Sanchez ended up on the DL with a left ankle sprain.
In 115 games this season, Schierholtz is hitting .278 with nine homers and 41 RBI.