Forced from Tuesday's loss to Toronto after three innings, Sabathia returned to New York for an MRI on Wednesday. Manager Joe Girardi says the team was happy with the results, but he will wait until returning home Friday before making a decision on Sabathia's next turn.
"When you have a guy that has a banged-up knee, you worry that there's more damage," Girardi said.
Sabathia has worn his current knee brace since the second half of 2015. Eligible for free agency at the conclusion of the World Series, the 17-year veteran is 9-5 with a 4.05 ERA in 19 starts.
"The key for him has been bringing stability back to the knee, and the brace has been a big part of that," Girardi said. "But when you're landing and you have pain every pitch, you're going to have a hard time. That's what we saw last night, so we've got to knock that out."
Girardi said rookie left-hander Jordan Montgomery is "probably the leading choice" to return from Triple-A Scranton/Wilkes-Barre if Sabathia is unavailable to face the Red Sox. Montgomery is 7-6 with a 4.05 ERA in 21 starts.
Montgomery was optioned to Triple-A on Sunday in an attempt to limit his innings, which New York wants to keep to about 180. Montgomery, who has pitched 115⅔ innings so far, set a career high with 139⅓ innings at Double-A Trenton and Scranton last year.
Girardi said outfielder Aaron Hicks (strained right oblique) is expected to come off the disabled list Friday. Hicks, who is batting .290 with 10 homers and 29 RBIs, has been out since June 25. He hit a two-run homer at Double-A Trenton on Tuesday, his first homer in seven rehab games.
Girardi also confirmed that first baseman Greg Bird (bruised right ankle) and second baseman Starlin Castro (strained right hamstring) should be ready to begin rehab assignments next week, with Bird's schedule slightly ahead of Castro's.
Outfielder Clint Frazier was scratched from Wednesday's lineup because of tightness in his oblique. Aaron Judge moved from designated hitter to right field, Chase Headley went from first base to DH, and Garrett Cooper entered the lineup at first base.