GREATER Western Sydney coach Leon Cameron has apologised to the AFL and the emergency umpire he approached during Sunday's loss to Fremantle at Domain Stadium.

The League has accepted his apology but is still determining whether or not the coach will be sanctioned.

Cameron left the coach's box twice during the game to personally query fourth umpire Nathan Williamson.

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His actions have since drawn criticism from the AFL Coach's Association as well as League CEO Gillon McLachlan, who said it was "not a good look" for the game.

The GWS coach rang AFL umpires boss Wayne Campbell and Williamson on Monday to apologise for the incident.

Head AFL umpires coach Hayden Kennedy said it was inappropriate for Cameron to have approached an umpire in that manner.

"There are guidelines and rules that govern these types of actions," Kennedy told AFL.com.au.

"I'm sure the AFL will deal with it in what they think is the most appropriate manner.

"I know that Leon has apologised to both the AFL umpiring department as well as the emergency umpire. It's terrific from Leon's point of view and we're really appreciative of that."

Veteran umpire Justin Schmitt, who is about to officiate his 300th game this weekend, said while umpires and coaches had some interaction before the game, it was unusual during the actual match.   

"I don't think that's something the coaches or the AFL want to see, so going forward I don’t think we'll see it again," Schmitt said.

Meanwhile, the AFL will trial a fourth field umpire during the round 19 clash between the Brisbane Lions and Gold Coast at the Gabba.

Schmitt said congestion and "density around the ball" has made the game more difficult for the umpires to adjudicate.

He said another pair of eyes would make it easier.

"We'd get a different perspective on things, different angles, [we would] be able to squeeze up and get more sets of eyes on contests where there are 20-30 players around the ball," Schmitt said.

"There's a much better chance of getting the right outcome." 

Kennedy said the umpiring department would love to make four field umpires a permanent fixture of the game going forward to ensure the game is adjudicated to the highest standard.