Alexis completed a transfer to Old Trafford on Monday as part of a deal that saw Henrikh Mkhitaryan move in the opposite direction to Arsenal.
Fans have been waiting in anticipation of seeing their latest signing turn out in the famous number 7 shirt and they could well get their wish as the Red Devils travel to Somerset.
"You know, because he’s in England for quite a long time, I think everybody knows the player he is," Mourinho said of his newest attacking addition.
"We got one of the best attacking players in the world and he’s very important for us because we want the best possible players.
"We go [to Yeovil] with a very strong team."
The United boss was also asked as to where he would deploy the Chilean, with Mourinho happy to report that he sees the 29-year-old as highly versatile.
"I've known him for many, many years, I was with him in Italy at Udinese, in Spain, when he was at Barcelona, in England, when he was at Arsenal, so our careers were almost made in the same countries simultaneously, so I know him very very well.
"I saw him play on the right, on the left, as a striker and behind the striker, these are Alexis’ positions.
"I saw him play different tactical systems, different philosophies of different managers, I saw him successful in every country with every manager and every position so he’s a player that becomes more than a player because of that motivation, he can play in four different positions."
United's FA Cup clash with Yoevil Town kicks off at 19:55 UK time.