Frenkie de Jong joined Barcelona from Ajax in 2019
The 25-year-old is new manager Erik ten Hag's summer transfer priority.
However, any potential deal is being hampered by a contractual issue involving De Jong and Barcelona.
The problem centres on wages De Jong deferred during the pandemic which are due to be repaid over four years.
De Jong delayed receiving the funds to help the financially troubled Catalan club and the money would have been given back over the course of a new four-year contract which is about to take effect.
De Jong is reluctant to leave Barca given what he feels he is owed.
United have consistently stressed they have alternatives should their attempts to sign the former Ajax man prove unsuccessful.
However, the fact chief executive Arnold and football director Murtough have chosen to fly in for face-to-face talks with Barca officials underlines the desire to sign De Jong.
Under normal circumstances, at least one of them would have been in Thailand, where United begin their pre-season preparations against Liverpool on Tuesday.
-- Courtesy of BBC Sport