The 31-year-old has been out of action since suffering a dislocated kneecap and rupturing his medial, anterior and posterior cruciate ligaments in March of last year.
It has now been confirmed that the centre-back will fly to Philadelphia on Sunday to continue his recovery.
"Bill Knowles came over a few months ago and so he is someone I've met already and spoken to about my injury alongside our medical team," Barker told the club's official website.
"I am grateful that the club and (head coach) Steve McClaren are allowing me to go out for two weeks. Bill is a top rehabilitation coach. I will have two tough weeks of work out there and I'm looking forward to it. I'm in a good place going out there thanks to the medical team here at Derby."
Barker has been with Derby since 2009.