St George Illawarra star forward Tyson Frizell has undergone testicle surgery after sustaining a blow to the groin in his side's opening round loss against the North Queensland Cowboys.

Frizell left the field after an attempted tackle on Cowboys' fullback Jordan Kahu early in the second half, with follow up scans leading to the second rower going under the knife.

AAP reports Frizell would be assessed before the side's Thursday night match against the South Sydney Rabbitohs in round two

"On Saturday night in our game against the North Queensland Cowboys, Tyson Frizell copped a blow to his testes," Dragons head of performance Nathan Pickworth told AAP.

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"Following the game, we investigated further with follow up scans which unfortunately resulted in surgery being performed in Townsville.

"Tyson this morning is in a good condition and in good spirits.

"We will update Red V members and fans further as more news comes to hand later in the week."