The first time Blue Jackets goaltender Steve Mason looked human this season was Jan. 3, in a 5-2 loss in St. Louis. The next day, general manager Scott Howson revealed that Mason had been feeling "a little under the weather" that night against the Blues. No big deal, the club reasoned.

But during the next few weeks, even as Mason put up extraordinary numbers that had national hockey columnists throwing the rookie's name in the NHL MVP race, there were infrequent whispers in the dressing room that Mason was suffering from a lingering cold, or perhaps the flu.

On Thursday, the Blue Jackets got word that Mason has mononucleosis, an energy-sapping viral infection than can linger for months.

"It's nice to know what it is," coach Ken Hitchcock said. "He felt poorly when we played (a recent trip) out West, and he didn't feel any better when we got back.

"No one can tell exactly when he started feeling it. But the best indication is it's been there for a while and the worst part is over."

The club has asked Mason not to discuss the illness with the media.

But his play did the talking Saturday. He allowed three goals on only eight shots and was pulled midway through the first period in a 7-3 loss to the Dallas Stars. It was the first time Mason has been pulled.

"A few minutes into the game, he was drained," Hitchcock said. "We talked to him before the game and he said his energy level was fine. But for whatever reason, after five or 10 minutes, he was just drained."

Mason has started 18 straight games for the Blue Jackets, the second longest current streak in the NHL. It's raising a question of whether the Blue Jackets are overplaying the 20-year-old.

Even after learning of the mononucleosis diagnosis Thursday, Mason made back-to-back starts Friday (vs. Ottawa) and Saturday (vs. Dallas). He was noticeably slow Saturday.

"It's pretty black and white," Hitchcock said. "If he doesn't feel good, we're not going to play him. If he doesn't have the energy, we're not going to put him in there.

"It's something we've been dealing with, and even now that we know what it is, we'll keep dealing with it as we have been. We're going to go 24 hours at a time, with practices and with games. It's up to him. If he's good, he'll go."

Hitchcock was asked if leaving the decision to play up to Mason is fair. Most goaltenders are notorious for wanting to play all 82 games. They often have to be forced out of the lineup in favor of the backup.

"A player is not going to tell a coach when he can't play," Hitchcock said. "He might not tell a teammate, either. But that's why the training staff has a great relationship with (Mason). He'll tell them the truth.

"We, as coaches, have a tendency to stick our noses in there. Well, I'm not going to do that. Whatever (trainer) Mike Vogt tells me, that's what we'll do."

Hitchcock would not rule out Mason starting against St. Louis on Tuesday in Nationwide Arena. He also would not rule out Mason starting both ends of back-to-back games this weekend vs. Pittsburgh and San Jose.

"He was feeling a lot better today," Hitchcock said.

Former Ohio State goaltender Mike Betz will join the Blue Jackets today in practice, Hitchcock said. And he'll likely be a familiar face for the next few weeks at least.

"We're going to give Mase the breaks he needs," Hitchcock said. "But we hope the worst of it is behind us now."

aportzline@dispatch.com