MONTREAL — These are uncharted waters Montreal Canadiens defenceman Andrei Markov is swimming in.

For 14 seasons, he’s been a pillar of stability, an offensive force, a ‘General’ — as head coach Michel Therrien has affectionately referred to him over the last three and a half seasons.

But in his 15th season, at age 37, Markov’s body isn’t cooperating with the mind that has always helped him navigate the NHL game with such precision.

“It happens to every player when they get to a certain age,” said Therrien after Montreal’s 4-1 loss to the Boston Bruins Tuesday. “For example, [then 40-year-old defenceman] Sergei Gonchar last year.

“It happens. He’s not done, but there’s going to be times — it’s going to be tougher.”

Times have been uncharacteristically tough for Markov of late.

It started when Therrien benched Markov for long stretches of the third period of a mid-December loss to the San Jose Sharks. The Russian rearguard then spent games on the team’s third pairing for a stretch before rejoining P.K. Subban on the top pairing last week.

Therrien admitted last week that he and defence coach Jean-Jacques Daigneault were consciously trying to limit Markov to 20-23 minutes of ice time per game, but he also acknowledged that the assignment would still require him to deal with the heavy burden of playing against top players on the opposition.

Markov has struggled to handle it.

For 26 minutes of an impeccable performance against the St. Louis Blues last Saturday, Markov was his old self, breaking up plays by being two steps ahead of them, passing the puck brilliantly as he always has.

But five seconds into minute-27, he coughed up a puck to Blues forward Robby Fabbri who set up Jori Lehtera for the overtime winner.

Markov played what Therrien referred to as a “phenomenal” game, against Chicago the following night — albeit in another losing effort for Montreal.

But Tuesday’s game against Boston was so far from Markov’s best.

There was this blunder Markov made on the game’s first goal — 13:08 into the first period — that had one reporter quip on twitter that Markov was minus-2 on the single play.

“I feel bad,” said Markov. “I’m responsible for that, and right now we can’t look for any excuses. That was my fault.”

What followed was a second period that saw Markov bobble the puck several times, including on the power play — where he’s done his best work throughout his career.

About his career, it’s worth revisiting if only to put this slide into context.

Just this past weekend, Markov passed Canadiens legend and seven-time Norris Trophy-winner Doug Harvey for games played in the team’s uniform. He’d have done it far sooner had it not been for three horrific injuries suffered from 2009-2012; the laceration of his Achilles tendon followed by consecutive ACL-tears that required reconstructive knee surgeries.

His pride has seen him fight through the adversity, as he collected 146 points in 257 games (including 50 in 81 last season) since the rash of injuries. That production has helped him become the third-highest scoring defenceman in Canadiens history with 515 points in 893 games.

But on Tuesday, none of that seemed to matter to more than a few fans at the Bell Centre who booed Markov loud enough to catch Therrien’s attention.

“I was disappointed by our few fans, who booed Andrei,” said Therrien. “This guy gives everything that he’s got for this hockey team over the years.

“It’s not a matter of will,” Therrien continued. “This guy is a true professional.”

But how much longer can Markov play at the level the Canadiens are paying him to play at? How much will his pride be dented by being relegated to a lesser role?

These are troubling questions to have to ask given the role Markov was supposed to play for this team, which was supposed to be closer to contending for the Stanley Cup this season but is now officially on the bubble of a playoff spot for the first time all year.

Markov is signed through the end of next season, and he carries an annual cap hit of $5.75 million.

The nights where things are going to “be tougher for him” are going to become more frequent.

That’s the type of adversity Markov has never faced before.