His teammates did.
According to several players McElroy confided in, the quarterback had been wrestling for days with the decision to tell the Jets' medical staff of his symptoms.
On Christmas night, McElroy visited wide receiver Clyde Gates in the hotel where the team stays before home games during the season. Gates had been diagnosed with a concussion earlier in the season, and listened to McElroy's concerns.
"He came to my room and we talked about it," Gates told ESPNNewYork.com. "He was hurting real bad. I was like, 'Bro, I know, I've been down that road already. I'm just saying you can't try to tough it out cause you going to end up hurting yourself. You've got to let everybody know how you really feel.' "
Left guard Matt Slauson was also aware of McElroy's condition.
"He definitely has that (warrior) mentality, but it got to the point where it was scaring him," Slauson said.
Slauson revealed to ESPNNewYork.com that he, like McElroy, had a concussion in either 2010 or 2011 that he didn't report to the Jets, and another in his senior season at Nebraska. Of the more recent concussion, Slauson said he got through it on his own.
"I didn't feel like it warranted (being reported)," Slauson said. "I was in bad shape, but I could focus on my plays. I figured I'd pop a couple of Aspirin and be fine."
McElroy experienced headaches during his morning lift at the Jets facility, and finally approached Jets trainers with his symptoms. Coach Rex Ryan immediately decided McElroy would not start when the Jets travel to Buffalo for the final game of the season on Sunday. In McElroy's place, Ryan again passed over Tim Tebow and went to former starter Mark Sanchez, who was benched after throwing four interceptions in Tennessee on Dec. 17.
Tebow said he could tell something wasn't right with McElroy even before the presumed starter was missing from the morning quarterback meeting.
"He didn't look exactly right at the beginning of the day," Tebow said. "So it wasn't long when we heard he went to the trainers and we heard what happened."
Ryan said McElroy should have been honest with the trainers about his condition, but seemed to understand that McElroy didn't want to give up a starting opportunity in a league where they don't come easily. Gates said that was probably a consideration for McElroy.
"It probably was a little pressure," Gates said. "I don't blame him, the position he was in, to start another game, any competitive player would've been like, 'I'm going to shake it off and make it work.' But, still, you got to be smart about it. I feel for him though. I understand how he feels, but you can't go against a concussion injury."
Ryan said "players need to be honest" given all the medical information about concussions available. Research shows that sustaining additional concussions before the brain heals is more damaging to a player.
"I think, hopefully, this will be an example to all the players," Ryan said. "Because the worst thing that could've happened is he would've gone out there with nobody knowing how he really felt and hurt himself."
"It affects everybody differently," Smith said. "One time it might be memory and motor skills. You never really know with a concussion. That's the problem with them: You don't really know how to diagnose them. You may feel a little funny but just think it's from the game."
Earlier this season, San Francisco quarterback Alex Smith self-reported a concussion and ultimately lost his starting job to replacement Colin Kaepernick. Tebow said that kind of information affects some players' minds when they are deciding what to report.
"You fight hard to earn something and you don't want to jeopardize that with an injury for sure," he said. "I think that's definitely something guys will think about."
Tebow said the idea of self-reporting concussions can be difficult for a player. He admitted that even he might not have always done it at times.
"I'm sure there's a few times in my career where I haven't made the smartest decision," Tebow said.
"I think it's hard, just being honest. I think it's hard for a competitor, even if you're feeling something to always report it," Tebow said. "I think that's probably the smart thing to do and it's what you want everybody to do, but that's not how you're trained as a competitor. You're trained to fight through it and be competitive and not let it phase you -- and that's not the smartest thing."
Information from ESPNNewYork.com's Rich Cimini was used in this report.