Mbappe started against Espanyol in Real Madrid's season opening 2-1 LaLiga win last weekend, but it was Espi who came off the bench to score a late winner, on his Los Blancos debut.
Real Madrid's decision to activate Espi's €25m release clause at Levante this summer - on the back of scoring 11 league goals there in his first-ever top-flight campaign - has slipped under the radar following a club record deal for Yan Doimande.
Espi adds aerial power to Mourinho's attack and the Portuguese coach insisted he can play with Mbappe if needed.
"I can see them playing together. Espí is a different type of player. The other day Espanyol were sitting deep and Kylian was trying to drop back for individual plays.
"I thought Carlos could be important then off the bench. Adding Trent and a 'giant' in the box increases our options."
Real Madrid take on Real Sociedad tonight in Mourinho's first home game in charge since returning to the Estado Bernabeu.