John Carlson, center, suffered an undisclosed “lower-body” injury. (Geoff Burke/USA TODAY Sports)

Washington defenseman John Carlson is doubtful to play in the Capitals’ game against the St. Louis Blues on Thursday night because of an undisclosed “lower-body” injury, Coach Barry Trotz said.

“He did some therapy stuff today and that,” Trotz said. “He got worked on yesterday and all the good stuff. I would say he’s doubtful just because he hasn’t skated for a couple days. We’ll make sure he’s healthy before we put him back in.”

Carlson didn’t play after the first period on Sunday afternoon against the Philadelphia Flyers, and though he traveled with the team to Pittsburgh on Monday, he missed his first game of the season. Carlson wasn’t on the ice for team’s optional morning skate in Pittsburgh on Monday or the practice in Arlington on Wednesday.

Trotz said Washington will consider recalling a defenseman for the two-game road trip. If a call-up were needed, it’s expected to be Aaron Ness. Trotz said on Monday that Carlson was “close” to being able to play again, considered day-to-day by the team.

“John’s improving and he may morning skate tomorrow,” Trotz said. “But I don’t have a definite on that.”

If Carlson weren’t playing, Taylor Chorney would be in the lineup. In Wednesday’s practice, Chorney skated on a pairing with Karl Alzner, Carlson’s usual partner. Matt Niskanen was on a pair with Dmitry Orlov, and Brooks Orpik was with Nate Schmidt.

Carlson left practice early Thursday afternoon, and the team said he was being evaluated for a lower-body injury. Trotz indicated Carlson’s ailment was not serious, saying that he just needed “a little maintenance” after Wednesday night’s game against the Penguins. Carlson played 20:42 in Friday’s game against Chicago.

On a Penguins power play in the third period on Wednesday night, Carlson blocked a Kris Letang shot with his leg, and when asked if that was related to him leaving practice early Thursday, Trotz said “it’s related from playing in a hockey game.”

Carlson leads the team in time on ice per game with 23:17, playing on the first power play and penalty kill. With him not on the ice on Sunday, Niskanen manned the top power play unit, and Schmidt was on the second unit.

Carlson missed 26 games last season with a broken ankle. He has five goals and 20 assists this season and has skated on a top defense pairing with Alzner. The Capitals have been the healthiest team in the league this season, as they’ve had just 11 man-games lost to injury.

Trotz said Washington won’t recall an extra forward for the road trip, going with the minimum of 12.

“We have airplanes and we can get people in,” Trotz said. “You can go four hours and go across the country.”