NHL referee Don Henderson is out indefinitely as he has been battling concussion symptoms since he was hit by Calgary Flames defenseman Dennis Wideman during a game last month, sources confirmed to ESPN on Friday.

In addition, a source told the Calgary Sun that Henderson, 47, has also had back pain since the hit on Jan. 27 and that "he still can't do anything because he hasn't gone two days symptom-free [from the concussion]. ... I don't think he's coming back anytime soon."

NHL commissioner Gary Bettman upheld Wideman's 20-game suspension Wednesday, but the ban could still be reduced, as the defenseman is appealing to a neutral arbitrator via the NHL Players' Association. Wideman has already missed eight games since being suspended, but he could be reimbursed for any time missed if the neutral arbitrator reduces the ban to a total lower than the amount of games he has sat out.

"I am left with the firm view that a significant suspension is appropriate," Bettman said in his ruling. "On-ice officials simply cannot be made the target of a player's frustration or anger. As noted above, the NHLPA observed that a reduced suspension is within the realm of possibility, though the Union did not suggest one. I do not see a basis for a lesser penalty, particularly given the severity of the conduct involved."

Linesman Don Henderson, who was injured after being hit from behind by Calgary's Dennis Wideman, is suing both Wideman and the Flames. Jeff McIntosh/The Canadian Press/AP Photos

Wideman, who had just taken a hit from Nashville winger Miikka Salomaki in the Jan. 27 game, said the cross-check on Henderson was unintentional and the result of a concussion that Wideman had suffered from the hit. He was not penalized during the game.

"I took a pretty good hit down in the corner and had some pretty good pain in my shoulder and neck," Wideman told reporters in Calgary that night. "I was just trying to get off the ice and kind of keeled over. At the last second, I looked up and saw [Henderson] and couldn't avoid it. I went up to Donnie and apologized to him on the ice.

"I didn't see him. I didn't know where to go and how to get out of the way. I've been around for a few years, and I think I've treated every official with the utmost respect, and I would never intentionally try to hit a linesman or a ref. It was completely unintentional, and I already apologized to him."

The source told the Sun that Henderson, who finished the game but spent the night in the hospital, had an MRI on Wednesday to see if any damage had been caused to his brain. The linesman, who has worked more than 1,200 NHL games since 1994, has not officiated an NHL game since the incident.

ESPN's Craig Custance and Pierre LeBrun contributed to this report.