Mayoral actually came off the bench for Zinedine Zidane's side in their 1-0 home victory versus Real Valladolid on Wednesday.
However, in terms of a starting berth for Madrid he is competing for the number nine spot with Karim Benzema, Luka Jovic, and Mariano Diaz.
The Spanish champions have been keen to offload at least one of Mayoral, Jovic, and Mariano this season, and they have got their wish after Mayoral completed a medical with Roma.
Roma were actually linked with Jovic this week but have opted for the Spaniard, with him joining on loan initially with the option for a permanent transfer.
Mayoral has been on loan at Levante for the past two seasons, scoring three goals in 2018/19 before more than doubling his tally in 2019/20 to eight goals in 34 appearances in La Liga.