Wellington Phoenix football coach Ernie Merrick's hoping the A-League will retrospectively punish the Western Sydney Wanderers player who left his defender Ben Sigmund concussed.

Photo: PHOTOSPORT

Sigmund collapsed early in the second half of the 2-1 loss at Parramatta with what were thought to be the effects of a week-long virus, but it's since emerged the former All White was also concussed from an earlier collision.

He's flown home and has been replaced by defensive midfielder Vinnie Lia for Thursday's game against Sydney FC, leaving Merrick fuming that no on-field action was taken against the Wanderers striker responsible.

Sigmund collapsed seemingly out of nowhere and looked in a bad way.

The 34-year-old former All Whites defender was immediately replaced by Louis Fenton, though Fenton later moved to right back, while Manny Muscat moved to centre back alongside captain Andrew Durante.

Merrick said Sigmund 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 and lamented the fact that returning All Whites international Michael McGlinchey was "exhausted" after his trip to Oman.

The coach 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," Merrick 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."

The Phoenix remain sixth on the A-League ladder despite the loss, while the Wanderers climb from fourth to third.

- AAP/RNZ