The centre-half has suffered another setback in his bid to return from the groin injury which has kept him out since September.
Robinson is now due to fly to America to see a specialist in a bid to solve the problem.
"It's obviously been an incredibly frustrating time for myself but I'm feeling positive," he told the club's official website.
"Until I see a specialist I'll have no idea how much longer I'm likely to be out for.
"But at this stage the most important thing is finding out what is causing this problem and finding a way to mend it."