Al Horford’s struggle to find mental equilibrium has been excruciating.

Amid the omnipresent media wanting to know his timetable for returning from the NBA’s concussion protocol program, internal pressure brewed by the Celtics’ uneven play in his absence, and his own personal doubts about what feels right and what most definitely doesn’t, Horford’s sense of readiness can change daily.

He’d missed nine straight games before finally returning to the lineup in last night’s matchup with the Detroit Pistons, the opener of a three-city Celtics road trip.

Any athlete wading through a concussion is desperate for more information. So Horford turned to Brian Scalabrine, the former Celtic and CSN announcer who wrestled with his own concussion issues — and an overriding urge to play through symptoms — prior to the 2009 playoffs.

The opportunity at hand was key to Scalabrine. Kevin Garnett had gone down for good with a knee injury, and Scalabrine had made seven straight starts when he caught an inadvertent elbow to the head from Dirk Nowitzki. Scalabrine was playing some of the best basketball of his career. The last thing he wanted was to fall out of Doc Rivers’ rotation, and the power forward admits he came back too early.

But Horford is a different case, Scalabrine said last week.

“He has to get it right. There’s no variable on that,” Scalabrine said. “And from the medical staff to Danny (Ainge) to wherever, you’ve got to get this right. The whole thing about getting multiples is scary.”

Getting it right — perhaps the most uncertain part of recovery — is the most elusive accomplishment of all.

Asked when a concussed athlete finally knows it’s time to get out, Scalabrine said: “When you go out there and play and nothing happens.”

The word that bothers Scalabrine the most is “multiples.” He discovered through meetings with neurologist Dr. Robert Cantu that he had suffered five concussions since his freshman year at Highline Community College in 1997. He had suffered three alone since January 2009.

Rivers told Scalabrine to not worry about playing — that his young family deserved more consideration than basketball — but the big forward listened to opportunity and returned.

“Then I barely got brushed and I got another one,” Scalabrine said.

The cautionary tale is stark enough. Scalabrine told Horford that if this was his first concussion, then he should take extra care not to get another one. The likelihood of another concussion rises with each “ding.”

“I told Al that everyone is going to have different symptoms. Things that I had, he didn’t feel. I had a sensitivity to light, and he had that, too,” Scalabrine said. “But my issue is, 'Al, if you get another one and your percentage goes up after the first one, then you could be out for a long, long time, not a couple of days. It shifts to a month after that, and you don’t want that — trust me on that one.' You’re constantly thinking, ‘What the heck is going on?’ You’re constantly seeing doctors. One is one and you deal with it. Getting multiples? That’s where it becomes a big, big issue.

“I’m sure there’s football players who are getting them every game. Multiple concussions is bad, bad news. One off here and there is not that big a deal.”

Scalabrine had another message for Horford: Don’t do what I did.

“I wanted to play. Leon Powe tears his ACL (in the playoffs) against Chicago, I went out there and said, ‘Forget it, man. I have a great opportunity to play,’ ” he said. “I averaged 20-something minutes a game in the playoffs. Should I have been out there? From my opinion? Yes. In the real life of the world, being completely cleared, probably no. But nothing was going to stop me from getting that opportunity to play. This is my livelihood.

“It’s a little bit different now because there’s so much info out there,” Scalabrine said. “They just made a movie about it three years ago — a super dark movie by the way. But for me it was about playing basketball and that’s it. I’m opportunistic in life, just trying to take advantage of situations. With Garnett it was really killing me. But the whole organization from Dr. Cantu to Ed Lacerte, Danny Ainge, they all kept the same message — ‘We don’t know a lot about this, but you have to be healthy.’ ”

That’s why Scalabrine wants Horford to heed his own uncertainty.

“It’s about getting through it,” Scalabrine said.

This week’s C’s timeline

Tomorrow, at Minnesota, 8 p.m. — The Timberwolves are probably the most intriguing young team in the NBA, and Karl-Anthony Townes is a future MVP. He’s already one of the best big men — not just best young big men — in the NBA. The Celtics will rest a lot easier if Horford and Jae Crowder are back by this game.

Wednesday, at Brooklyn, 7:30 p.m. — The Nets are supposed to be busy feathering the Celtics’ nest for the 2016 NBA draft. Instead, they’re playing competitive basketball. As Isaiah Thomas recently said, he doesn’t keep track of draft picks. But the Celtics have an especially vested interest tonight.

Friday, vs. San Antonio, 1 p.m. — A special Thanksgiving weekend matinee. The Celtics have to hope it doesn’t turn into a Black Friday event against the longest running power in the NBA, albeit now without Tim Duncan.

Knicks’ Porzingis learns the ropes as he climbs

Kristaps Porzingis may never put enough muscle on his 7-foot-3 frame to bang with the tougher wide bodies in this league.

But the Knicks forward is also learning to make his long, skinny build work in the most physical basketball league on earth. As evidenced by his skillful 35-point performance during a win over a big Detroit team Wednesday, Porzingis may be able to make this work on his terms.

“I think last year when I watched him, obviously we just played against him two times, but it seemed like he’d drive a lot and then throw kind of a wild shot up and that might have been because of strength,” first-year Knicks coach Jeff Hornacek said of Porzingis. “He got knocked off his positioning. I don’t see that this year. When he drives he’s been pretty solid, so I think his strength he worked on over the summer helped him. He’s making his shots and guys are looking for him. If he gets the ball anywhere in the lane he should be able to get a shot off. He’s so tall.”

As the Celtics demonstrated with Marcus Smart, though, Porzingis can have significant trouble with smaller, stronger players.

“One night we had a rough time when they switched small guys onto him,” said Hornacek. “We went over a couple of things. Hopefully they’ll get better at that. When teams try to switch we have to be able to take advantage. (The Celtics will) put Marcus Smart on him, just to get into his legs and keep him from shooting 3’s. That’s when we’ve got to go in the post and get him a mismatch there. KP is learning his moves. Our coaches are working with him on that.”