MELBOURNE'S Tomas Bugg has been reported for an incident that left Sydney’s Callum Mills concussed and out of the game in Friday night's clash at the MCG.

Bugg punched Mills in the side of the face with his left fist in the opening stages of the match. 

The incident happened four minutes into the game and behind play on the Swans' forward flank as the Demons were kicking in.

WATCH: 'Embarrassed' Bugg will 'cop the consequences'

Mills was left sprawled on the ground and was still and stunned for at least 10 seconds before he moved. Bugg was reported immediately.

A free kick, originally awarded to the Swans, was reversed when Tom Papley ran in and floored Bugg in defence of his downed teammate after other Swans had already remonstrated.

Mills left the field and was given a concussion test in the rooms, which he subsequently failed.

He returned to the bench at the 19-minute mark of the term and took a seat in the back row with his evening declared over by the medical staff.

Bugg played out the quarter with a torn jumper, which happened when Mills' teammates remonstrated, but was clearly rattled and ended the term with just one disposal to his name.

The pair had been pushing and shoving in the lead up to the incident after lining up on each other.

The Demons went on to kick four goals to one and led by 10 points at quarter-time.

Melbourne captain Nathan Jones, who is sidelined with a quad injury, told Channel Seven at half-time his teammate's actions were "a terrible look for the game".

"I think 'Buggy' would be livid with himself - he'd be very remorseful," Jones said.

"It will run its course during the week obviously and will probably be well-publicised, but I'm sure Buggy is just hoping that Mills is OK.

"I know Buggy really well and I'm sure there was no intent to hurt, but obviously he's struck him on the chin and unfortunately it doesn't look like Mills is going to take any further part."

The incident is sure to draw extra attention after a week dominated by Bachar Houli’s hit on Jed Lamb and the subsequent Tribunal fall-out.