The Red Devils conceded the joint-fewest goals of any side in the Premier League last season, 35 goals from 38 games, but fared much worse against Champions League and Europa League opposition.
Indeed, continental campaigns which ended with elimination at the hands of Wolfsburg and Liverpool respectively saw United concede 13 times from ten games – losing three of them.
And Mourinho reportedly believes that is due to the lack of experience in the Old Trafford outfit’s backline with Chris Smalling currently United’s most seasoned defender at the age of 26.
United have already signed Eric Bailly from Villarreal this summer but the versatile Ivory Coast international is just 22 years of age.
Mourinho appears determined to bring in a real leader, although The Daily Record fail to mention potential candidates available via the transfer market.