Pens captain Sidney Crosby, who has been diagnosed with a concussion, skated in full gear on Thursday at UPMC Lemieux Sports Complex.
"'Sid' did skate this morning and he's in the process of rehabbing," head coach Mike Sullivan said. "We'll leave it at that."
Sullivan did not reveal Crosby's availability for Game 5 of the Second Round series, which takes place Saturday night at Verizon Center in Washington, D.C., saying only, "It's a day-to-day process and we're taking each day as it comes."
Crosby suffered the concussion in Game 3 of the Pens' Second Round series against the Capitals following a pair of head blows from Washington's Alex Ovechkin and Matt Niskanen.
Crosby missed Pittsburgh's 3-2 Game 4 victory on Wednesday night at PPG Paints Arena. He also missed seven games at the beginning of the 2016-17 season with a concussion.