The Cowboys injury toll is mounting on the eve of Origin after it was revealed that centre Tautau Moga is out for the season after he injured his anterior cruciate ligament in the Pacific Test two weeks ago.

The initial diagnosis was a grade one medial ligament injury after tangling with Tongan Sika Manu, but the amount of swelling around his right knee meant that doctors could not get a proper reading until it had reduced.

It is a devastating blow for the already crippled Cowboys who have lost Jason Taumalolo and Scott Bolton in recent weeks.

Moga is still in hospital recovering from successful surgery, but questions remain over his ability to play a substantial career with all three injuries occurring on the right knee.

Coach Paul Green holds little doubt that the 21-year-old will return to the playing field once more.

"It's pretty tragic news for Tau," he said on Thursday.

"He's only just gotten out of hospital today, had the operation yesterday so we will just play it by ear for now and in the short term it is just about him getting over that operation.

"The way the rehab and resources that clubs have available to them, it's certainly not out of the question by any stretch. He's still a young guy so he has time on his side."

Coming up through the ranks Moga was billed as the next Israel Folau, but injuries have meant that the Brisbane junior has not played a substantial amount of football since entering the competition in 2012.

Moga was emerging as North Queensland's brightest prospect among an ageing back-line after holding a consistent spot with the Cowboys since he arrived at the club mid-year.