The Penguins center, who has missed the past 16 games, had been playing through the injury before having surgery, which was expected to keep him out at least six weeks.
"We're just taking each day as it comes," Sullivan said after practice in Calgary. "We're certainly encouraged with his progress to this point. The fact that he's skating again and has skated for a handful of [days] is encouraging."
However, there is no timetable for a return for Crosby, who has 17 points (five goals, 12 assists) in 17 games this season.
"He's making progress in his rehab process. We're encouraged by where he's at," Sullivan said. "As he gets closer, we'll update you."
The Penguins (19-10-4), who have gone 9-4-3 without Crosby, their captain, hold the first wild card into the Stanley Cup Playoffs from the Eastern Conference ahead of their game against the Calgary Flames at Scotiabank Saddledome on Tuesday (9 p.m. ET; ESPN+, SNW, ATTSN-PT, NHL.TV).
