Castro hurt his leg while trying to beat a ground ball that ended the third inning of the Yankees' 6-5 win.
Neither manager Joe Girardi nor Castro were certain if Castro would end up on the disabled list. Castro will have an MRI Tuesday, and then the team will make a determination.
"I don't think it is that bad," Castro said.
There was no timetable for his recovery.
There were reports out of Scranton that highly regarded Triple-A utility man Tyler Wade was called up, but Girardi said he was unaware, if that were true.
Castro missed Sunday's game because of a cortisone shot to alleviate the nuisance of a sore right wrist.
Castro, 27, has had a first half that might make him worthy of an AL All-Star selection. He is batting .313 with 12 homers and 45 RBIs. If he is selected, this would be his fourth time as an All-Star and first with the Yankees.
The Yankees were already without Aaron Hicks on Monday. Hicks was placed on the DL with a right oblique strain that could keep him out for three or four weeks. CC Sabathia, Greg Bird and Adam Warren are all also on the DL.
Yankees DH Matt Holliday missed his second game in a row Monday. The Yankees were trying to figure out what was wrong with him, as manager Joe Girardi said Holliday feels achy and under the weather.
Prior to Monday's game, the Yankees got one player back, as Jacoby Ellsbury returned from the DL after being shelved with a concussion.
Castro leaves with hamstring injury
Starlin Castro hits a slow ground ball to third base, and while running to first, he comes up limping. Castro leaves the game with a strained right hamstring.