The Red Devils registered a 1-0 victory over FC Rostov in the Europa League clash at Old Trafford on 16 March. They will travel to Riverside Stadium to face Middlesbrough at midday (12pm GMT) in the league tie on 19 March, which is 62 hours after their last match ended against the Russian side.
Mourinho admitted United have a lot of enemies due to the hectic fixture list and the club legend Roy Keane slammed the comments made by the Portuguese tactician. However, the former Real Madrid and Chelsea manager has received support from Liverpool boss, who was in a similar situation with the Reds when they were playing in the Europa League last season.
"I heard what Jose Mourinho said and what the pundits think about it. Last season we had the same experience. It was really hard. We played Villarreal and then Swansea at 12," Klopp explained, as quoted by the Liverpool Echo.
"If they want to help, you cannot do that, you should not do that. I know it is contracted, but that's only 12pm or 4pm? Don't play then.
"Don't make it more difficult than it should be. I really understand. We thought the same last season. We thought it was really hard. That was an experience. This year we could not use it but next year hopefully we can use it. That's how the job is."
United have already played 18 matches across all competitions during this calendar year. Out of those, only two of them have ended in a defeat and those losses came against Hull City (in the EFL Cup) and a 1-0 defeat to Chelsea in the FA Cup quarter-final.