Walker underwent two operations on his finger and knee but both were described as minor and should not affect his pre-season training.
The 29-year-old started four matches during the 2011 RBS 6 Nations scoring a try in his last appearance against Italy, but will face renewed competition for a starting berth from the likes of Max Evans, Sean Lamont, Simon Danielli and Jack Cuthbert.
All have been included in Andy Robinson's provisional 40-man World Cup training squad which will be cut to 30 following the August warm-up matches.
And Walker was able to breathe a sigh of relief that he will be able to take part in those matches against Ireland and Italy after Towers handed him a clean bill of health.
He said: "Nikki has had a couple of small procedures, one to address a tendon injury to his finger and a keyhole procedure for a cartilage issue in the knee.
"He will start his rehab with the Ospreys medical team over the next few weeks before joining up with the Scotland squad to complete rehab and continue his Rugby World Cup preparations."