On the eve of college basketball’s preseason, the Arizona Wildcats received what could be the final piece of a powerhouse rotation.

The NCAA ruled forward Zach Peters eligible immediately, with four years to play, just a day after UA coach Sean Miller wondered aloud why it was taking so long to rule on his request to avoid the standard redshirt season required of transfers.

If Peters is cleared to play medically after suffering multiple concussions that led to his departure from Kansas last winter, the forward from Plano, Texas, is expected to be a key reserve forward for the Wildcats.

At 6-foot-10 and 240 pounds, Peters is a tough-minded player with the ability to stretch defenses with his outside shooting. That’s a niche the Wildcats lost when Grant Jerrett opted for the NBA draft last April after his freshman season.

Miller said there was “no question” Peters would play a solid role for the Wildcats, but there were plenty of questions about whether Peters would be allowed to play. Not only is he still rehabilitating after his concussions, still staying out of full-contact drills, but he went all summer without knowing if the NCAA would let him play anyway.

“I’ve tried to remain patient throughout this process, and today’s news is definitely a relief,” Peters said in a UA statement. “I’ve been making strides physically with the goal of getting back to full competition, and, right now, it’s about honoring that process. I’m excited to keep improving and it’s great to be able to put my focus on the season ahead.”

Peters transferred under unusual circumstances, having left Kansas last winter after suffering five concussions over the previous two years. Peters suffered a concussion during a LeBron James camp during the summer of 2011 and then during his senior football season in high school the next fall.

His father, Tim, said Zach then suffered two concussions late in the summer of 2012 at Kansas and, in the fall of 2012, was wearing a protective helmet when he took another blow that required stitches. He left Kansas by mid-December.

Before he left, Zach Peters said he signed a form indicating he could not transfer for medical reasons, which may have slowed his appeal process down.

Peters’ request for immediate eligibility was contingent on if the NCAA deemed he left Kansas for reasons out of his control. Miller said UA presented a “very honest assessment of the situation that it wasn’t under his control,” while Miller and Tim Peters said Kansas also backed Peters’ request.

“With Zach’s scenario we were very optimistic,” Tim Peters said Thursday night via telephone. “Kansas supported it. We thought the NCAA would do the right thing and we’re excited.”

Still, Tim Peters said the NCAA ruling was a “great surprise because we had no clue that this was going to go on six weeks or two more months.”

Miller didn’t know what would happen, either, saying during UA’s preseason media day Wednesday that the NCAA was “0 for 5” in dates it had indicated a ruling would have been issued by.

“It’s probably as simple as one person picking up a piece of paper, walking 50 feet and dropping it off on a desk, and that (next) person picking up the paper and putting a check mark on it,” Miller said Wednesday. “But we’re not there yet.”

They found out Thursday, when the NCAA informed Arizona and Arizona in turn informed Peters’ family. UA issued a news release at 5:45 p.m. Thursday, with full practices scheduled to begin today.

“Today’s news from the NCAA is very exciting for Zach and his family, as well as our basketball program,” Miller said in a statement. “There was a lot of effort and cooperation that went into this waiver process. We’d like to thank the NCAA, the University of Kansas and many members of the Arizona athletics family for their tireless efforts to make this a reality.”

Miller said Peters has participated in everything except full-contact drills so far, but was optimistic that he would be able to soon. So is Peters.

“I do everything except for live play against each other,” Peters said during the media day Wednesday. “Right now we’re really close.”

Tim Peters said his son was first cleared by a physician in Texas back in February, having made dramatic gains since he left Kansas under difficult circumstances after the fall semester.

“His brain healed to the point where (when he left Kansas), he couldn’t multiply two times negative five — but by the end of January, he was at the 87th percentile of all college freshmen,” Tim Peters said. “So the brain snapped back, and the next part was ocular, balancing of his eyes. They’re saying, ‘Let’s keep him out of contact until we get those eyes where we want them.’ ”

To that end, with assistance from UA medical staff, Peters was assessed in Pittsburgh by concussion specialist Mickey Collins, and still takes computer eye tests daily.

“Dr. Collins said ‘You can take a blow and there’s no repercussions,’ ” Tim Peters said. “That’s the great news. He’s not fragile. He’s not gonna break. And contact is kind of his middle name.”

Sportswriter for the Arizona Daily Star covering Arizona Wildcats basketball