Milan - Inter Milan completed the signing of Danish international midfielder Christian Eriksen from Tottenham Hotspur on Tuesday.
Eriksen made 305 appearance for Spurs after joining from Ajax in 2013, scoring 69 goals.
However, a contract standoff with the club meant a departure was inevitable either this month or on a free transfer at the end of the season.
"The only thing I can say is Eriksen, since I arrive, he is behaving in a very, very professional way, with me and the team," Mourinho said after Saturday's 1-1 draw at Southampton.
Antonio Conte's men are three points behind Juve at the top of the table, but their title challenge has stumbled of late with three consecutive draws.