The red noncontact jersey that Patrice Bergeron wore Tuesday at Warrior Ice Arena classified him as off-limits to his teammates’ thumps. Bergeron made his exit when the Bruins initiated battle drills late in practice. By the end-of-session conditioning sprints, Bergeron had been off the ice and into the recovery stage to rehabilitate his mystery ailment. 

Those signs indicated that while Bergeron is improving, the lower-body injury that has cost him five games may add to that total.  

“I feel everything is getting better now,’’ Bergeron said. “I feel stronger on the ice and more comfortable. Hopefully game action is closer rather than later.’’ 

It is not just that the Bruins have missed a world-class center during their 2-3-0 stagger out of the blocks. Bergeron touches the game and the lineup to such a deep degree that the trickle-down effect manifests itself in many troublesome ways: 

■ Brad Marchand, half of the league’s best 200-foot duo, is without his partner. Marchand is good on his own, but not as good as when No. 37 is on his right flank. 

■ Riley Nash is a versatile depth forward who can kill penalties, take draws, play center and wing, and be responsible defensively. But being a No. 1 center is not included on Nash’s résumé. 

■ The Bruins were comfortable giving Anders Bjork top-line duty because he’d have Bergeron as a babysitter. Without Bergeron serving as a security blanket, the explosive rookie has yet to express the entirety of his game. 

■ David Krejci is best utilized as a No. 2 center with David Pastrnak as his right wing. They can take advantage of second-pairing defensemen. When Bruce Cassidy had to load up his first line with Marchand, Krejci, and Pastrnak, the rest of the lineup was compromised. 

■ Ryan Spooner has enough trouble being a consistent third-line center. Spooner (0-1—1, four shots, 13:16 average ice time) has done nothing to merit classification as a top-two pivot. 

Despite Bergeron’s limitations, Cassidy welcomed his best player back to practice because of the ways in which it helped stabilize his lineup. Cassidy returned Krejci and Pastrnak back to the second line with Jake DeBrusk.

David Backes, sidelined because of diverticulitis, practiced for the first time since his diagnosis, manning the right wing on the third line with Nash and Tim Schaller.  

With Spooner missing because of an undisclosed injury, Sean Kuraly centered the fourth line between the ghostly Matt Beleskey and Frank Vatrano, both scoreless this season. Austin Czarnik and Danton Heinen were assigned to Providence. 

“Some of the games that have gotten away from us, those guys are glue guys who would have added that element to keep us on the rails without the game getting away,’’ Cassidy said of Bergeron, Backes, and fellow right-shot forward Noel Acciari (finger).

“Other nights, you lose guys in your lineup when you just need offense or hard defending. Some of their leadership, obviously. They’re all good players. But most of them, you know what they’re bringing every night: the north-south game.’’ 

The Bruins reset some of their expectations of Backes, in whom they invested five years and $30 million on July 1, 2016. They identified him as the No. 3 right wing, one with penalty-killing, faceoff, and power-play duties as part of his workload. In turn, Backes adjusted his offseason training to emphasize speed and agility over havoc-wreaking. 

So when a loss of appetite and stomach pain led to hospitalization, it was an especially damaging blow. The veteran was eager to initiate a career reboot after a turbulent first season out of St. Louis. 

“Sitting down at the hospital, watching a standard-definition TV with the Bruins playing the Predators, and I can see the Garden from my hospital room — that’s a tough emotional swing to swallow,’’ Backes said Tuesday.

“When you’re at home, it’s never easy when you feel like you worked all summer and kind of changed yourself a little bit to have a lot of success this season. Then to have that false start to begin with, it’s tough to deal with mentally.

“But coming back and having extra energy today, the past is the past. We’ve got to look what the next step is to try and be the best player I can be to help us win games.’’ 

Backes didn’t eat for several days. He was on a liquid diet. He lost 10 pounds. Doctors told him not to exercise for a week following the diagnosis. So while Cassidy termed Backes and Bergeron as possibilities for Thursday’s game against Vancouver, both are still dealing with curbs that would make NHL action unhealthy and possibly dangerous. 

Every team deals with injuries. It is a fact of life, especially given the accelerated pace of today’s game. By the time Bergeron and Backes are cleared, it’s a good bet one or several of their teammates will be asking for ice bags. But the absences have hurt the Bruins to a greater degree because of the experience, coolness, and hard-on-pucks approach that Bergeron and Backes display.  

Deficiencies have flared up in every area: creating offense, limiting chances, stopping pucks. But the Bruins’ most alarming shortcoming has been their softness on the puck. Bergeron and Backes make life harder for opponents.  

Without them, the Bruins have been easy to play against. 

Fluto Shinzawa can be reached at fshinzawa@globe.com. Follow him on Twitter @GlobeFluto.