ST. LOUIS – For many who picked the Boston Bruins to win the Stanley Cup Final over the St. Louis Blues, depth was one of the major reasons why.

As the series has gone on, however, that depth has been chipped away at.

Following Game 4, the Bruins may have suffered their biggest loss yet, both figuratively and literally.

Six-foot-nine defenseman Zdeno Chara, the team’s 42-year-old captain, was reported to have suffered a broken jaw when Brayden Schenn’s second period shot attempt ramped up off of Chara’s stick and into his cheek. Bleeding from the mouth, he left the ice with the assistance of the team’s training staff.

Initially, fears that the injury was serious seemed to be relaxed when the 21-year vet returned to the bench for the third period wearing a full face shield, but that he didn’t take a single shift afterwards let on that something wasn’t right.

“He was advised not to return to play,” Bruins head coach Bruce Cassidy said after Game 4.

“He had some stitches, probably some dental work in the near future. He wanted to come out to the bench and be with his teammates, and that’s why he was out there, but I don’t know his status for Game 5. … I can’t say whether he’d play or not, I have no idea.”

Since then, reports have surfaced that Chara suffered a broken jaw on the play and is unlikely to play in Boston on Thursday and, most likely, the rest of the series. With the Bruins having already lost another defenseman, Matt Grzelcyk, to an apparent upper-body injury after being boarded by Oskar Sundqvist in Game 2, the team is now down to their eighth defenseman.

That, most likely, will be Steven Kampfer, but Cassidy does have other options; he listed Urho Vakkanainen, Jeremy Lauzon, and Jakub Zboril as other players who may get the opportunity to slot into Chara’s spot on Thursday.

The problem, of course, is that trio combines for only 20 games worth of NHL experience.

“We’d have to look at Kampfer, obviously, first,” Cassidy said. “He’s been the only one playing for us in the playoffs, but he is another left stick.”

Vakkanainen did skate with the team on Wednesday, but incredibly, it would seem that Grzelcyk could potentially be an option; he also skated on Wednesday, but was still in concussion protocol and was wearing a red non-contact jersey.

“When he gets cleared, he’ll be ready to go, but whether that’s by [Thursday] or not, I couldn’t tell you,” Cassidy told reporters in Boston on Wednesday.