"Over the last few weeks we have been trying to manage the situation but the way we have been trying to manage it has not given us any answers," Fergie has said.
"In the past 10 days we have sent him to a specialist in Sweden, to a specialist in London and he is now in Colorado at the moment seeing Mr Steadman.
"He is of course a very well regarded and well respected doctor and what we are trying to do now is get to the root of it because the poor lad has been frustrated and patient and we have never really got to the bottom of his problem.
"That is why we are now sending him to the best people available to get a general opinion on where we go from here."
Hargreaves has made just 25 starts for United's first team since joining the club from Bayern Munich in August 2007.