Pittsburgh Penguins captain Sidney Crosby has started exercising in his bid to return from concussion-like symptoms, but the National Hockey League team has no idea when he will be back. Penguins coach Dan Bylsma had little to say about the Canadian superstar, who has played only eight games this season after suffering a concussion last January and taking a blow to the head last month that brought back problems. \"He is in light exercise. He is exercising,\" Bylsma said of Crosby. \"What that is, in terms of heart rate and activity, is different on different days. That’s where Sid is in his rehab right now.\" On Tuesday, Crosby missed his 13th game since returning to the injured list after a 10-month layoff. The Penguins led the Eastern Conference when Crosby was hurt and now they are in eighth place as the season reaches its midpoint. The 24-year-old center said he is again nagged by the same problems that ended his 2010-2011 season early. \"I have to make sure with these sort of things that I\'m careful and making sure I\'m 100 percent before coming back,\" Crosby said. Crosby has become the NHL\'s signature player, leading the Penguins to the 2009 Stanley Cup, and became a Canadian hero after scoring the golden goal in over-time to win the Winter Olympic crown for Canada last year at Vancouver. Crosby scored twice in his return game November 23 against the New York Islanders but did not score again before being injured again.