LOWELL — All Drew Baker could do was sit and watch, patiently but anxiously with his hands on his face, as his teammates on the Lincoln-Sudbury Regional boys’ hockey team did what they had for so long wanted to do: capture a Division 2 North sectional title and clinch a spot in Sunday’s state championship game at TD Garden.

The Warriors had come close before. L-S advanced to the North semifinal in 2013, when Baker and the rest of this year’s seniors were mere freshmen, and again in 2014. Last season, L-S suffered a first-round playoff exit.

Now here is Lincoln-Sudbury making a run — as the North’s No. 7 seed to meet South champ Medfield, and Baker, in the waning weeks of his high school career, has been stuck on the sideline with a concussion for the past month and a half.

That included the North final Monday at the Tsongas Center. Lincoln-Sudbury edged top-seeded and previously undefeated Marblehead, 3-2, on the strength of two goals from senior Eric Holden. Baker was physically present, but instead of getting in on pregame introductions, goal celebrations, and the final frenzied moments as L-S held on for a win, he sat in the last row of Section 123 with the Warriors’ other (mostly healthy, mostly underclassmen) scratches.

Minutes later, in a quiet corner in the bowels of Tsongas, with a suit and tie instead of pads and puck, Baker expressed optimism that with the progress he had been making, his neurologist would allow him to play in Sunday’s final.

“It’s been aw —“ Baker started before pausing for a few seconds, seemingly stuck between the team’s success being awesome and his relegation to observer status being awful. “Yeah, no, it’s been awful.’’

It’s been awful since Feb. 3, when Baker — second on the team in points with eight goals and six assists, behind only Holden (24 goals, 16 assists) — got hurt against Boston Latin at Northeastern’s Matthews Arena. He was hit from behind and caught the boards at a bad angle. He struggled off the ice, vomited in the locker room, and went home early. The next day, a trip to the hospital made official what seemed obvious: a concussion, Baker’s third in four years.

The next couple of weeks were bad. Baker did not go to school. He wore sunglasses wherever he went. He laid in bed, lights out and blinds drawn. Constant headaches and dizziness and increased sensitivity to light — exactly what you might think of when you read “concussion-like symptoms’’ — were hallmarks of his days.

He wasn’t getting better fast, and with the regular season ending in late February and the postseason potentially ending any given game after that, the neurologist told him he was done.

“It was probably one of the worst things I’ve ever heard,’’ Baker said. “I didn’t even know what to say. I walked out with my mom and didn’t even say a word, knowing the sport I loved was gone and I couldn’t do anything about it.’’

Baker, as badly as he wanted to play, knew better than to push it.

The climate surrounding brain injuries is increasingly careful, and Lincoln-Sudbury’s win over Marblehead came on the same day an NFL executive, for the first time, acknowledged a link between playing football and long-term brain damage, a development seen as a significant win for concussion awareness.

Baker had two concussions before this one, the worst one.

“Before, I would always try to get back when I could,’’ Baker said. “Now I’m really like, ‘You know what? I need my brain.’’’

The better-safe-than-sorry approach differs greatly from the one that might’ve been taken when, say, Lincoln-Sudbury coach Hal Gill played at Nashoba Regional in Bolton in the early 1990s, followed by a four years at Providence College and a 16-year National Hockey League career.

“I don’t know how it would’ve been handled in the past,’’ said Gill, who has guided L-S to the Garden in his first season as varsity head coach. “I assume they would’ve just let him play and go.

“[Baker] has a lot of speed, plays well on both sides of the puck. It’s tough, because we went through a hard time when we missed him. I give the guys in the room a lot of credit. A lot of guys stepped up.’’

Lincoln-Sudbury lost the Boston Latin game and the next game too, but only once since then. Baker’s injury was one in a series the Warriors suffered that tested — and revealed — their depth.

Baker eventually started attending games again, including three playoff contests in a row at the Chelmsford Forum, the site of Lincoln-Sudbury’s season-ending losses the previous three years.

The Warriors knew they’d have to get by the Chelmsford stage — and all the way to the Garden — for Baker to have a chance to come back.

“I can only imagine that’s been really tough for him,’’ said Holden, who met Baker when the two were preschoolers taking learn-to-skate classes. “Everybody has been able to look to him as a guy who is staying positive through all the stuff he’s had to go through. We can translate that to the ice, meaning we have to think about the next play, focus on the next shift, no matter what happens on the ice.

Baker will head to Quinnipiac University in the fall, and he’ll major in biology with tentative intentions of pursuing a career in the medicine or sports science fields, an interest fueled by his many injuries — the trio of concussions, plus a few broken bones (wrist, thumb, ankle).

First, though, there is the matter of his final high school days.

Shortly after the win against Marblehead, Baker approached Gill to begin negotiating a ramp-up in activity that would, in a best-case scenario, culminate in Baker skating onto the ice at the Garden on Sunday.

Baker was cautiously optimistic. Gill was a little more cautious, maybe a little less optimistic. Before getting into the nitty-gritty of the week’s schedule, the 6-foot-7, thoroughly bearded, scally-capped coach enveloped the 5-foot-10, less thoroughly bearded athlete in an embrace.

“These kids battle hard,’’ Gill said. “You hate to see these things happen.’’

Tim Healey can be reached at timbhealey@gmail.com. Follow him on Twitter @timbhealey.