The former Bundesliga defender turned coach was scathing about the Jamaican sprint superstar's attempt to break into football and questioned why he was trialling with Central Coast Mariners.

And he insisted that the money spent on Bolt could be better spent on allowing coaches to have seven subs to pick from on match days instead,

"I know him only as a brilliant sprinter, not a footballer," said Kurz, 49, today. "I think the aim for the league must be to improve young Australian players and not bring a sprinter into this position."

Bolt has already trained with Kurz's former side Borussia Dortmund, but the veteran coach dismissed the world record holder's chances of breaking into the big time there.

"In Germany, the quality is too high," he said. "For the 1. Bundesliga, you cannot run for your whole life and then think, you're 32, you can play for the Bundesliga. No chance.

"I am interested to see what is the next step for Usain Bolt but for sure he must have the quality to play. He is fast enough but I don't know if he is good on the ball or not.

"If you want to improve the league then you must bring quality and he must have a higher quality than the players that are here. That for me is the point.

"If it is only to bring more supporters on game day, it is for me not right. I'd spend the money on other things."

He added: "Why not a game day squad for 18 players and then you can put two young players in the squad and then I can give them game time?

"That's what the league needs. They need strong, good Australian players because the NPL is not strong enough for them to improve.

"They have to improve in the A-League."

He called on the FFA to allow clubs to field bigger benches, with an emphasis on youth players and force sides to pay them more.

"Maybe spend money from the Federation to make squads two players bigger and then you have to put two or three or four young players in your squad.," he said. "Then for sure they will have game time..."