The Bruins’ third line had just found its rhythm. Last Saturday at TD Garden, Jordan Caron and Rich Peverley assisted on Chris Kelly’s first-period goal.

“They found the back of the net,” said Patrice Bergeron. “But they also had some time in the offensive zone by moving their feet, reading off each other, winning battles in corners. It just seemed like the whole line was clicking.”

Now they’ll have to find their pace all over again.

Kelly missed Tuesday’s game because of an injured left knee. Because of swelling around the knee, the Bruins have not been able to determine the severity of the injury. Kelly, who was with the team in Pittsburgh, will be reevaluated upon the team’s return to Boston.

“We’re anticipating and hoping for minor,” said coach Claude Julien. “But for me to predict right now would be careless.”

Kelly was hurt at 0:42 of Monday’s second period against Ottawa at Scotiabank Place when he collided with former teammate Chris Neil. Neil was not penalized and will not face supplemental discipline.

The Bruins could have recalled a center from Providence. Ryan Spooner leads that team with 10 goals and 31 assists in 47 games. Spooner made his NHL debut earlier this season when he centered the fourth line against Montreal Feb. 6.

Instead, the Bruins shifted Peverley from right wing to center. Peverley played 14:21 and assisted on Zdeno Chara’s power-play goal. Peverly won 10 of 13 faceoffs.

“I’ve played center before,” Peverley said. “Chris and I switch off a lot, too. It’s not like it’s that foreign for me.”