Sydney Roosters back-rower Aiden Guerra will be sidelined until next month after suffering a broken cheekbone in Sunday's 20-12 loss to Cronulla at Allianz Stadium.

Guerra is believed to have suffered the injury just before half-time when he rounded up a runaway Valentine Holmes and slowed the Sharks fullback enough for Mitchell Pearce to make what was effectively a try-saving tackle.

Down and out: Michael Ennis checks on Aidan Guerra after the Rooster went down in back play. Credit:Getty Images

Guerra stayed down in back play and was taken from the field for a concussion assessment but Roosters officials confirmed he had suffered a broken cheekbone and would undergo surgery on Monday to insert a plate.