The former Lockerbie Academy pupil, who played with the Annan RFC’s under 18 side for several seasons, was badly injured in March.
Dunbar, 25, who plays centre for Glasgow Warriors, ruptured his anterior cruciate ligament in training during the RBS Six Nations.
After an operation to repair the damage, Dunbar has been trying to get back to match fitness with the Rugby World Cup looming later this year.
In a bid to be ready for the autumn tournament, Dunbar – who grew up in Johnstonebridge – is travelling to Philadelphia for a three week recovery plan under leading rehab specialist Bill Knowles.
He will then return to the Scotland camp for further assessment and the next stage of his rehabilitation
Paul McGinley, the Scottish Rugby head of performance medical, said: “We are pleased to say that Alex remains on schedule at this stage and that, 14-weeks down the line, he is now in the right place for this trip to the States.
“Evidence suggests that the earliest you could expect somebody to safely recover from ACL reconstruction is around six months, and that is tight; but that’s the timescale to which we are working if he is to feature in the Rugby World Cup.”
He added: “We’re doing everything we can to give him the best chance of keeping to that timeline and making the competition, while paying close attention to the his long-term welfare.”
Mr McGinley added: “There’s another, crucial, rehabilitation phase coming up, with a view to giving him game time before the World Cup, providing we can stick to the recovery schedule.”
Last year Dunbar scored a tremendous second-half brace of tries as Scotland posted their first win in the RBS 6 Nations Championship by 21-20 against Italy in Rome.
He is regarded as one of most talented young midfielders in the game and has been one of the stars of the Glasgow Warriors side.