NORTH Melbourne defender Aaron Mullett is likely to be sidelined until mid-May after having surgery to repair a torn labrum in his left shoulder.

On Tuesday, North said the 22-year-old was expected to be sidelined until round seven after going under the knife on Monday.

The Roos play Essendon on Friday, May 15 in round seven.

Mullett had a few shoulder issues at the end of last year but the Roos were hopeful he would get through 2015 unscathed.

But North’s director of sports science and training services Steve Saunders said Mullett had suffered further damage over past two months.

"The consensus was that Aaron would be fine to get through another season and we'd review him again at the end of the year," Saunders told the club’s website.

"New symptoms developed, we've reinvestigated these and found new pathology in his shoulder joint."

Mullett's injury is a setback to his hopes of re-establishing himself in North's best 22 this year.

The dashing half-back emerged as one of North's most exciting young players in 2013, finishing equal-fourth in the NAB Rising Star Award and 10th in the Roos' best and fairest.

But Mullett had an up-and-down season last year following an injury-disrupted pre-season. He played 17 games, but was dropped five times and left out of all of North's three finals.