New York Yankees ace James Paxton underwent an MRI on Saturday morning and said he was diagnosed with "nerve irritation," which apparently caused the tightness in his left glute on Friday night.
Paxton said he took medication and doesn't expect it to be an issue heading into the playoffs.
Paxton was removed from Friday night's start against the Texas Rangers after one inning. His departure ended his career-best streak of victories in 10 consecutive starts.
The left-hander is 15-6 with a 3.73 ERA this season and has not lost a start since July 26.
ESPN's Marly Rivera contributed to this report.