Despite a bright start to life in Europe’s premier club competition, the Red Devils finished third in a tough group that featured two of last season’s semi-finalists; RB Leipzig and Paris Saint Germain.
Ole Gunnar Solskjaer’s men lost 3-2 to the German opposition on Tuesday, dropping down to the Europa League in the process.
The quality within the United set up saw them score a group-high 15 goals but losses to Istanbul Basaksehir and PSG at home saw them miss out on qualification despite needing just a point in their final two games to progress.
Tottenham are also favourites to win the Europa League but Mourinho believes United’s arrival makes things harder for his side.
"Manchester United become one of the top favourites to win the competition," the Portuguese told a press conference on Wednesday.
“The teams that drop from the Champions League are strong and normally don’t belong to the level of the Europa League.
“United are one of the top teams. The group was very hard with Paris Saint-Germain and Leipzig. We knew it was not going to be easy for any of them.”
Mourinho led Manchester United to the Europa League title in 2017, defeating Ajax Amsterdam 2-0 in the final.