The 20-time English champions appointed the 53-year-old as their new manager on Friday morning ending months of speculation linking United with the Portuguese coach.
While Louis van Gaal guided the Red Devils to FA Cup glory, United finished outside the Premier League’s top four and won’t feature in next season’s Champions League.
Keane won seven Premier League titles, two FA Cups and the Champions League as a United player during a decorated career at Old Trafford between 1993 and 2005.
However, the former Red Devils captain isn’t a fan of the new United manager, although Keane has backed Mourinho to bring back a winning mentality.
“He was available, fantastic CV and it seems like a good fit, but maybe he is not for me,” Keane told ITV Sport.
“He is not my cup of tea. I found him really irritating when I coached against him, but that is just a personal thing, but working at Man Utd is all about winning and his CV will tell you he is a winner.”
United have appointed David Moyes, Van Gaal and current boss Mourinho since Sir Alex Ferguson’s retirement in 2013 following the club’s 13th Premier League title success.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news