COMMERCE CITY — Over the past eight years, Rapids center back Drew Moor has been one of Major League Soccer’s ironmen, playing in 235 of 245 games and twice playing every minute of every game.

That streak ended abruptly Aug. 17 when the Rapids’ captain ruptured the anterior cruciate ligament in his right knee on a routine play at D.C. United, putting him in the unfamiliar position of long-term rehabilitation after major surgery.

Moor, who had never had a significant injury, has returned to normal training but has yet to regain enough confidence in the knee’s strength to play without hesitation. His return to game action may be a month away.

“They’ve kind of left it up to me,” Moor said. “I need to be ready to go mentally before I step back into a game. I would hope May, at the latest.”

Coach Pablo Mastroeni said Moor “looks great” in training, but he understands the mental hurdle.

“I’m very aware and cognizant of the mental aspect of injury, having gone through a lot myself,” Mastroeni said. “We touch base every 10 days to see where he’s at, making sure when he’s back it’s because he’s coming back on his terms.”

Fellow center back Shane O’Neill was already out with a sprained MCL last season when Moor was injured in a noncontact play, leaving a big hole in the center of the defense. The Rapids went winless the rest of the season with eight losses — including a 6-0 drubbing at Los Angeles — and two draws.

“It was one of those freak plays,” Moor said. “I’m running full speed one way, marking a guy on the ball and he cuts it. I plant and try to turn real fast and all the pressure went straight to the knee. It was probably a play I’ve done a thousand times and, for some reason, this time it was ready to go.”

Moor said the knee feels good.

“Physically I’m probably just about there,” Moor said. “It’s a little bit more the mental side of it, getting back into gamelike situations in training — tackles, cutting, the game-like movements that you can’t simulate on a practice field.”

Last year the Rapids were thin at that position, and the defense fell into disarray without its two starters. Reinforcements arrived in the offseason: MLS veteran Bobby Burling, a 6-foot-5 graduate of Lewis-Palmer High School, and Axel Sjoberg, an impressive rookie from Sweden via Marquette University who stands 6-7.

Thus the Rapids will have four capable center backs when Moor is ready to go. O’Neill will have departures because of duties with the U.S. under-23 team — essentially the 2016 Olympic team — but Mastroeni will have some tough decisions to make.

“When I get back, I’m going to have a spot to win back,” Moor said. “It’s not my spot just because I’m healthy. I will have, at that point, been out seven-plus, eight-plus months. It’s good that we are deep, because there is no rush (for his return). It’s a position we filled in because we needed it, and I couldn’t be happier. The competition’s fantastic, and it will hopefully only increase when I am ready to step back on the field.”

John Meyer: jmeyer@denverpost.com or twitter.com/johnmeyer