"In the middle of the game, he went to the cage to take some swings and took a swing and felt some soreness in his side," Rockies manager Jim Tracy said. "He was treated last night as the game was going on, came back in today and is still sore enough to where he's not able to participate."
Melvin Mora, who started at third base on Friday night -- because of the pitching matchup, not Stewart's injury -- was at third again on Saturday for the Rockies.
Tracy said Stewart was listed as day-to-day.
Stewart has started 100 games for the Rockies this year, all at third base. Saturday will be Mora's 27th start at the position. Stewart is hitting .278 with five doubles, seven homers and 16 RBIs with a .504 slugging percentage since the All-Star break. Mora was 2-for-4 with an RBI on Friday and was hitting .311 at Coors Field this year entering Saturday.