The pair have clashed on numerous occasions over the past decade or so, emanating from their time in charge of Liverpool and Chelsea when the Reds came out on top in a feisty Champions League semi-final tie.
Benitez was unwilling to discuss his relationship with Mourinho ahead of this weekend's Old Trafford showdown, however, insisting that he is instead more focused on stopping the Red Devils' attacking talents.
"We are playing against Manchester United. It is not important who the managers are," he told reporters. "[Mourinho] is a good manager who has won a lot. I'm more concerned about [Romelu] Lukaku, [Juan] Mata and [Marcus] Rashford.
"They are a massive club who, as always, have spent a lot of money and are doing well. They have to compete for everything. As always we will try to do our best to get three points if we can, but we know it will be difficult."