The initial news of the day for the Bruins — a contract extension for forward Rich Peverley — was overshadowed quickly yesterday by a troubling sight: top center David Krejci leaving the practice ice with an apparent leg injury. With the team doing 5-on-5 battle drills, the Bruins' No. 1 trio was on a line rush when Krejci suddenly stopped skating and hunched over in pain. One observer thought he might have caught a skate edge on the ice, which can cause injuries. Krejci sat on the bench for several minutes with trainer Derek Repucci attending to his left leg, then slowly skated off to the medical room. The Bruins offered little information, with coach Claude Julien unwilling even to confirm that it was a lower-body problem. "I can't really tell you the severity of it now," said Julien after practice. "He's being looked at."