The 39-year-old singer appeared to shade Swift, his ex-girlfriend, in a since-deleted tweet on her 27th birthday.
"Tuesday, December 13 may be the lamest day of the year, conceptually," he reportedly wrote to his 836,000 followers.
Mayer quickly deleted the tweet, and also wrote and deleted a followup post, according to E! News. He claimed in the later tweet that his original post wasn't about Swift.
"NOPE. No. Nuh-uh. People I am 39. I am deleting those tweets. Come right at me for doing so. Absolutely no shade," he wrote.
Mayer and Swift split in 2010 after a few months of dating. Mayer told Rolling Stone in 2012 that the song Swift wrote and released about their breakup, "Dear John," was "a really lousy thing for her to do."
"It made me feel terrible," he admitted. "Because I didn't deserve it. I'm pretty good at taking accountability now, and I never did anything to deserve that."
"I was really caught off-guard, and it really humiliated me at a time when I'd already been dressed down. I mean, how would you feel if, at the lowest you've ever been, someone kicked you even lower?" the star added.
Mayer and Swift reportedly avoided each other at Drake's 30th birthday party in October. Several members of Swift's squad, including Gigi Hadid, Karlie Kloss and Martha Hunt, were among the stars to wish the singer a happy birthday Tuesday.