Former AFL champion Paul Roos has defended running onto the field to come to the aid of an injured under-16 player who was hit off the ball, saying he couldn't just "stand on the sidelines as a coach and let that happen".

Ex-Sydney coach Roos found himself in the headlines after becoming involved in the aftermath of a clash during the junior match on Sunday.

That incident, where one of Roos' players suffered bruised ribs, is now the subject of an official investigation.

Roos now coaches the Eastern Suburbs under-16 team and admitted he ran onto the field after his player was hurt in the match against the Newtown Suns.

The AFL NSW/ACT said there were no reports from the match, but revealed there is now an official inquiry.

Roos said he had spoken to league officials previously about on-field incidents.

"I've spoken to the AFL about it and I know the AFL are concerned, as we all are," he told the Fox Sports program On The Couch.

"Certainly I've seen ... some incidents I'd rather not see on a footy field."

AFL NSW/ACT released a statement earlier on Monday, saying the AFL Greater Sydney Juniors were conducting an investigation into the incident because of an alleged code of conduct breach.

The investigation is expected to take no more than a week and AFL NSW/ACT would not say who is under scrutiny.

The injured player is Darcy Cordell, the son of Swans media manager Jenny McAsey, .

Roos wants the coach of a team to be able to go onto the field if one of his players is injured.

"There are varying degrees of views about what's going to happen, what happened," Roos said.

"Maybe I need to speak to the AFL about the protocols.

"I just can't stand on the sidelines as a coach and let that happen, in terms of the boy himself.

"I immediately reacted as the coach and I've since learnt the coach is actually not allowed to go onto the ground ... maybe I need to be up to speed on the rules."

Roos also admitted he spoke to the opposition player who allegedly caused the injury.

"I mentioned to the other team `who did it?' and to the boy's credit, he put his hand up," Roos said.

"I think I said `why?' and then the opposition runner came up, clearly he was offended by the fact I was talking to the players, the umpires were there.

"We eventually got Darcy off the field and as we were walking off, I asked the guy whether he'd spoken to the boy and he obviously took offence to that as well."

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