The goalie left after the first period of a 4-3 overtime loss to the New Jersey Devils on Thursday. He appeared to get injured making a save on Devils forward Nico Hischier 5:57 into the period and was on the ice for several minutes but remained in the game.
"It's a hard hit. It's a heavy hit," Sabres coach Ralph Krueger said before a 3-0 loss to the Philadelphia Flyers on Saturday. "In the best case we'll get him back in a month. A huge loss at this point in our season, especially coming off the tail end of that New Jersey game, which was clearly his strongest performance of the season (41 saves in a 4-1 win Tuesday). To see him get a lower-body injury that will take him out for a minimum one month is a hard hit. We're still digesting that and we're going to work with Linus to get him up to speed as quick as possible, but it's a long-term injury."
Ullmark was 5-4-2 with a 2.44 goals-against average and a .919 save percentage in 12 games this season.
Carter Hutton made 36 saves Saturday and backed up Jonas Johansson, who made 35 saves in a 3-0 loss to the Flyers on Sunday.
"It [stinks], obviously," Hutton said. "I think [Ullmark has] been our best player all year. He's been a big-time difference maker. It's frustrating. A guy I've been with for three years, you see him kind of come into his own and he's worked hard on and off the rink. It's obviously a tough time."
NHL.com independent correspondent Heather Engel contributed to this report
