Kyle Busch has admitted he "went too far" when he expressed satisfaction at Ryan Newman losing his NASCAR Sprint Cup seat during an outspoken post-race interview at New Hampshire Motor Speedway last weekend.
Busch also referred to Newman as an "ogre" and "the biggest stupid idiot out there" during the media gathering, according to USA Today.
Newman is hunting for a new drive for 2014 after Stewart-Haas announced it would release him to make way for Kevin Harvick alongside team boss Tony Stewart and Danica Patrick.
When Busch's comments were put to him by Sirius XM Radio, Newman described his rival as "not very bright".
Busch used his Twitter account to express his regret over bringing Newman's job situation into the spat.
"I was upset because I felt RN [Newman] raced me poorly, making contact and causing damage to my right front fender that affected the handling on my racecar," Busch wrote.
"This isn't the first time that I've been raced poorly by RN either, which added to my frustration.
"All this built up and allowed my emotions to spill over for how I felt.
"I'm not sorry for how I feel in those moments, but could have expressed it better and certainly my comments about someone's livelihood went too far."
Joe Gibbs Toyota driver Busch finished second to Brian Vickers in the Loudon race, while Newman went out in a crash triggered by Busch's brother Kurt being tapped by his JGR team-mate Matt Kenseth.