The Red Devils were linked with a big-money bid for the Colombia international in the January transfer window.
However, United didn’t make a move for the former Monaco playmaker, but Rodriguez continues to be linked with a switch to Old Trafford.
According to reports over the past week, Los Blancos are ready to sell the South American after an unconvincing 18 months at The Bernabeu.
Speaking to RTE Sport, former United midfielder Dunphy insisted that Rodriguez is overpriced at £80m after Madrid paid £80m to Monaco for the playmaker’s services.
“James cost £80m after playing outstanding well for Colombia in the World Cup,” Dunphy told RTE Sport.
“The president bought him. He is useless. The problem Zidane will face is that the president bought this guy.”
Rodriguez has only stated 11 La Liga games this season under Zidane’s predecessor Rafael Benitez and the Madrid legend.
The 24-year-old playmaker has scored five goals and has made six assists in 15 appearances in the Spanish top flight.
United have also been linked with a move for Madrid forward Gareth Bale over the past 12 months.
MORE: The latest football news