Sydney forward Gary Rohan has been knocked out after a sickening collision with Carlton's Sam Rowe at the MCG on Saturday afternoon.

Rohan has been taken to hospital for precautionary scans, but is awake and talking. It is believed he has been cleared of any serious injury. 

Midway through the third quarter, with Carlton building a lead, Rohan showed great courage to run with the flight of the ball to contest an aerial ball.

However, after coming into contact with Rowe – who approached the contest from the opposite direction – Rohan landed awkwardly on the back of his neck.

The 25-year-old laid unconscious and motionless for about a minute as the motorised stretcher was immediately brought onto the field.

Play was held up for five minutes as Rohan was carefully removed from the turf.

The Swans look set to be without Rohan for next week's clash with the Brisbane Lions at the SCG and coach John Longmire said it was difficult to watch the incident from the coaches' box.

 "From my understanding he's having precautionary scans. He's moving OK, he's awake and he's having precautionary scans," he said. 

"It obviously didn't look good and it looked as though he was in a bit of trouble for quite a while. That's the thing you notice. Normally when a player cops that sort of hit they're able to get up pretty quickly but he certainly didn't look like he was moving too flash." 

The motorised medical cart sped onto the field to attend to Rohan before the umpire had called a halt to play after the incident, which drew some queries from commentators, but Longmire said he did not notice its early appearance.