Ullmark is 9-6-3 with a .917 save percentage in 20 games this season. He is scheduled to become an unrestricted free agent this summer, though general manager Kevyn Adams said Monday that the team hopes to keep him in the fold moving forward.
Dustin Tokarski made his fifth start of the season on Thursday in Ullmark's absence, stopping 27 shots against Washington to earn his first NHL victory since 2015. Michael Houser, who has not played in the NHL, served as Tokarski's backup.
Granato said the team is looking to integrate goaltending prospect Ukko-Pekka Luukkonen into the NHL roster but is still determining a timeline for his potential recall. Luukkonen has been dealing with a minor lower-body injury that forced him to miss Rochester's game on Wednesday.
Luukkonen, a second-round pick in 2017, is 7-5-3 in 14 games with Rochester this season.
"Today's an important day to determine when he'll be integrated with us," Granato said.
The Sabres are also without Carter Hutton, who has been out since March 24 with a lower-body injury. Granato said Hutton has resumed skating on his own but there is no timetable for his return.
Granato also provided injury updates on forwards Kyle Okposo and Riley Sheahan, both of whom missed practice on Friday. Sheahan is considered day-to-day after sustaining an upper-body injury against Boston on Tuesday. Okposo is still being evaluated by doctors after he was hit in the head with a shot on Thursday.