"He is a player who we believe has all the attributes. He is very strong physically and very fast," the former Chelsea manager, who replaced Dutchman Louis van Gaal in May, told the club's website (www.manutd.com) on Wednesday.
"It's not so easy to find a fast player when you have quite a big body; he's a heavy guy, a tall boy who's really fast," said Mourinho, who was presented at United on Tuesday.
The 22-year-old Ivory Coast player was in a Villarreal back four that conceded only 35 goals in 38 league matches during the 2015-16 campaign and Mourinho is certain he can easily fit at right-back as well as central defence.
"He comes from a Spanish culture where the first phases (of play) are important so technically he's very good," the 53-year-old added.
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"For some periods, he played right-back and, because playing in the right-back position demands more from an attacking point of view, it's good for a centre-back to play some periods as a right-back."
"My only question mark at the moment is one I have to help him delete – the question mark of someone who has never played at such a big club with so many responsibilities and so many expectations.
However, Mourinho said he was not sure if Bailly would be ready straight away to play at the level required by United.
"So is Eric ready to come here and start performing from day one? I don’t know. It is a question mark but my job is to delete that question mark as soon as possible and give him the stature, brain and personality to play for Manchester United," he said.
Bailly also has 15 caps for Ivory Coast and was part of their 2015 Africa Cup of Nations-winning squad.
(Reporting by Ian Rodricks in Bengaluru; Editing by Ken Ferris)
