A run over the line has delivered winger Alex Johnston a knockout blow for South Sydney's annual Good Friday clash.

The Torres Strait Islander will be forced out next round against Canterbury, suffering a mild concussion in the throes of being denied a critical try in the 73rd minute.

The last-gasp tackle on Johnston left the all-time Rabbitohs' leading scorer lying on the turf until teammates arrived.

"I think he's in a bit of strife here," commentator Cam Smith told the TV audience.

"There's a big collision up in the north-west corner.

"But he (Johnson) drops the ball there."

The grade-one concussion that occurred on Friday night against Melbourne Storm has left Johnston unavailable to play across the next 11 days, under the new season's head injury assessment (HIA) protocols.

The 28-year-old rose with a large welt forming near his right eye after colliding heads with Storm fullback Nick Meaney.

Johnston also continued to look groggy while the video referee checked the grounding of the ball.

Meaney was able to knock the ball free from Johnston among all of the commotion of a thrilling finish at Accor Stadium in Sydney.

South's trainers led Johnston to the bench before ruling the speedster out of the dying minutes of the match where the Storm eked out a 18-10 win.

The visitors had continued to soak up prolonged periods camped on their line late in the second half.

Johnston also had a rough start to the match, missing a tackle on the edge after Storm recruit Will Warbrick powered over the top to score in the corner.

Indigenous teammate Cody Walker was the focus of the Rabbitohs' attack, scoring the first of their two tries of the contest.