BOSTON (CBS) – While one notable Bruin was absent for Monday’s ceremony at the White House, forward Nathan Horton was in attendance.

Horton, though, is out against Washington Tuesday night due to what general manager Peter Chiarelli termed as a “mild concussion.”

“These things are day to day. So I would say it’s day to day. It might not be. There’s that gray area. You take your ImPACT test. You see how it is the following day. Then you make that determination. He’s in that gray area there,” Chiarelli told the Boston Globe’s Fluto Shinzawa after the event Monday.

Horton was hurt during the second period of Sunday’s win over the Flyers when he was hit from the right side by Tom Sestito. He did not play in the third period or overtime of that game.

Horton suffered a severe concussion when he was leveled by Vancouver’s Aaron Rome in Game 3 of the Stanley Cup Finals last June.

With Horton out, Rich Peverley will likely take his place on the first line with Milan Lucic and David Krejci. In that instance, Zach Hammill would take the open spot on the third line alongside Benoit Pouliot and Chris Kelly.

Horton has 17 goals and 15 assists in 46 games.