The 32-year-old has spent the last six-plus seasons in Calgary after signing as a free agent on July 2, 2008. Glencross has tallied 114 goals and 128 assists for the Flames.
Glencross, who played his college hockey at Alaska-Anchorage, has also spent time with the Anaheim Ducks, Columbus Blue Jackets and Edmonton Oilers. He has nine goals and 19 assists in 53 games this season.
The Capitals host the Toronto Maple Leafs at 7 p.m. on Sunday, while the Flames are off until March 3 when they visit the Philadelphia Flyers.