"I thought, 'blow it!'" he said, and headed to Carlaw Park - which was "just around the corner" - to do a few sprints and test his recovery, only to be caught in the act by some league players who suddenly showed up.
"They asked, 'What the hell are you doing here, you are not a league player,'" he smiled, adding "They let me off."
Confident he was up to the task, Erceg put his hand up and was put on a plane flight south on the Monday for the game at Athletic Park.
The New Zealand Maori side featured a couple of highly respected Far North players; Peter Smith from Kaikohe (the brother of Johnny Smith, who Erceg described as "one of the greatest centres New Zealand had ever produced" but ruled out through injury) and Brownie "Nau" Cherrington from the Bay of Islands.
Cherrington asked Erceg to play on the left wing while he'd play on the right. Shortly after kickoff the New Zealand Maori side lost Smith with a fractured collarbone and had to complete the match with 14 men on the pitch.
"Our flanker had to play on the wing. Those days you didn't have any replacements," said Erceg, recalling being given the unenviable job of marking Ken Jones, who had also represented Britain in sprinting at the Olympics.
"He was fast," Erceg said. "I shadowed him all day. He scored one try, I was able to score one try."
The New Zealand Maori eventually lost the match 14-9.
The British Isles under Dr Karl Mullen won 17 of their 23 matches on the 1950 tour, drawing the first test 9-9 with the other three won by New Zealand.
The following year Erceg was selected to go on the All Blacks' tour to Australia. He ended up playing three tests that year and one more with the national side in 1952.
Erceg said he would probably not attend the Barbarians game in Whangarei tomorrow, the Lions vs New Zealand Maori clash in Rotorua on June 17 and the Lions vs All Blacks' test at Eden Park on June 24 (with all former All Blacks having been invited by the NZRU to attend a special dinner beforehand).
Instead, he'd likely end up - quite happily - watching all the games from the comfort of his living room.