ST KILDA midfielder Seb Ross has undergone successful surgery for a high-grade hamstring tear suffered in Saturday's NAB Challenge win over Essendon.  

Ross, who was not initially expected to have surgery, will miss 10-12 weeks. 

The 21-year-old was primed to take on more responsibility as an inside midfielder this year to help fill the void left by champion Lenny Hayes. 

Fellow youngster Daniel Markworth has also undergone surgery to repair his dislocated shoulder, which was injured at training last week.  

Markworth will be sidelined for an indefinite period, with his return date to be mapped out in more detail once his rehabilitation has progressed. 

The 22-year-old, who is yet to debut, has suffered a long run of bad luck, including a hamstring injury that ended his 2014 season after round 15.

The Saints have now lost five players to hamstring injuries this pre-season.

Veteran Farren Ray, who also required surgery to repair a hamstring rupture, has been ruled out for 12-14 weeks.

Shane Savage and Jack Billings could be sidelined for up to a month with hamstring strains.

Dylan Roberton, meanwhile, missed the opening NAB Challenge match with hamstring soreness.