Hes got 8 goals and 1 assits in the CL this year. Thats better than the likes of Kane, Sterling, Son, Benzema, Mbappe, and Salah and that are players in their prime playing for much better clubs.
And of course we can groom him and Greenwod at the same time. We have 4 attacking players covering 3 spots FFS. Right now Greenwood isn't being "groomed" as much as hes being thrown out there because we literally have no one else with Martial injured.
And yes i have seen him play. He terrorized Koulibaly all game when they played Napoli and hes one of the best CB's around now. Hes got pace, acceleration, strikers instinct, height, strength and good finishing abilities. We would be stupid not to go for him