From NHL.com:

PITTSBURGH -- Penguins star Sidney Crosby is optimistic about returning fully healthy for next season, but acknowledges he recently had a setback in his recovery from a concussion. 

Crosby, who didn’t play this season after Jan. 5, stopped skating with his teammates during off-day practices and morning skates midway through the Penguins’ seven-game playoff series loss to Tampa Bay because he began experiencing concussion-related symptoms. 

Previously, Crosby said those included headaches that made it impossible to take part in any physical activity. 

Crosby still has not resumed working out and intends to remain sidelined for an indefinite period. 

"I was working out and skating, but had a little bit of symptoms so I had to take a step back," Crosby said Friday, two days after the Penguins' season ended. "All the stuff that comes with it. Up to that point the progression had gone pretty well, but at the same time I still wasn't ready. 

"(It's) frustrating. My expectation was that I wouldn't play, but I was trying to make sure that if there was any chance and it was possible to come back, that I was ready and did everything I could to be ready for that. It's frustrating and disappointing. You can't really control any of that. All I can control is what I was doing off the ice and trying to rehab. Unfortunately it didn't work out."