Wellington coach Ernie Merrick has revealed he was in the dark about Ben Sigmund's persisting virus when he took the field against Western Sydney on Saturday.
Sigmund collapsed seemingly out of nowhere during the second half of the Phoenix's 2-1 loss at Pirtek Stadium and looked in a bad way.
He was immediately replaced by Louis Fenton.
Merrick said the 34-year-old defender had been suffering from a "really bad virus" all week but didn't let on to his coach it was still affecting him.
"We knew he had a virus, he said he was over the virus. But he did speak to the doctor before the game which I wasn't really aware of," Merrick said.
"He got double vision and started fainting so he collapsed.
"And I think he had a head collision as well."
"Ben is really a tough character, ex-rugby player. He would never admit to being under the weather.
"Had we known, we'd have made the change earlier. But he's not going to admit it and I quite like that about Ben.
"I wish more players were like that, really tough."
Merrick said there were no positives to be taken from the thrilling match, naming the Wanderers the better side and lamenting the fact that returning Kiwi international Michael McGlinchey was "exhausted" after his trip to Oman.
He added that new forward Jeffrey Sarpong is still "not quite with it" in high-energy matches despite the ex-Ajax and NAC Breda product playing his best game yet last week in the 4-2 demolition of Adelaide.
"It was just one of those days," he said.
"Having said all that, I was disappointed we conceded again from a corner kick and we keep giving them away.
"It was tough to come here and get a win and the Wanderers are playing high-spirited, competitive football.
"You can see they're really keen to get a win at home and we just didn't have the same energy."