Under fire ... Sam Ayoub.

Sam Ayoub ... manages some of the game's biggest names. Photo: Nick Moir

The police case against rugby league player agent Sam Ayoub has been dealt a blow after a magistrate ruled that a crucial witness cannot give evidence because he might incriminate himself.

Mr Ayoub, who manages some of the game's biggest names, has been charged with dishonestly obtaining financial advantage by deception over bets placed on the North Queensland Cowboys v Bulldogs game in August 2010.

In that game Bulldogs forward Ryan Tandy - whom Mr Ayoub managed - deliberately dropped the ball from the kick-off and then gave away a penalty in front of his own posts.

Arrested . . . Ryan Tandy.

Ryan Tandy ... was managed by Sam Ayoub. Photo: Brendan Esposito

It is alleged that Tandy, Mr Ayoub and a number of their associates had placed substantial bets on the Bulldogs scoring first in the game via a penalty goal.

In the opening of the trial in the Downing Centre Local Court today, the court heard that Mr Ayoub had used an associate, former Parramatta Toyota Cup player, Brad Murray, to place bets on his behalf, and that Mr Murray would be a key witness in the trial.

However, the lawyers for Mr Ayoub and Mr Murray said he could not be questioned in the hearing because he had the same charge pending against him over bets he had made for himself on the game.

Changed his story ... Brad Murray.

Brad Murray ... risk of self-incrimination. Photo: Dean Sewell

Any evidence he gave could be used against him in his own pending trial on these charges.

This afternoon, magistrate Antony Townsden found that Mr Murray was not required to give evidence because it was possible he would incriminate himself if he did so.

"When the competing considerations are taken into account, it is not in the interests of justice that the witness should not be compelled to give evidence," he said.

The decision is a major blow to the prosecution case against Mr Ayoub because it says that all but one of the $700 worth of bets he placed on the game were placed through Mr Murray.

It is alleged that Mr Ayoub placed only one $90 bet on the game personally. This bet is now what the police rely on to prove the charge.