COLORADO SPRINGS, Colo. (AP) — Jason Brown won’t defend his U.S. figure skating title because of a back strain.

The 21-year-old Brown could still petition for a spot on the Americans’ world championship team, but he doesn’t know yet whether he’d be healthy enough to do so.

Brown made the 2014 Olympic squad, finishing ninth, then won his first U.S. title last year. He said there wasn’t one moment when he hurt his back.

“It was gradually getting worse all season,” Brown said on a conference call Thursday.

He pulled out of NHK Trophy in late November and rested for a couple of weeks, hoping to be ready for the U.S. championships, which start Jan. 21 in Minnesota. But the injury flared up again recently in training.

Brown expects to be off the ice “for some time” and doesn’t have a schedule for his return. Doctors have told him he should be able to make a full recovery.

The world championships begin March 30 in Boston. He was fourth at last year’s worlds, the best showing by an American man since Evan Lysacek won in 2009, though Brown was well out of the bronze medal position.

He has been working to add a consistent quadruple jump to his programs, but Brown insists the injury wasn’t the result of any particular element.

With Brown out, Max Aaron, the 2013 U.S. champion, is the likely favorite. In October, Aaron became the first American man in six years to win at Skate America, where Brown was third.