Vin Diesel recently announced that he might be playing another Marvel character other than arguably one of the more beloved characters in the MCU, Groot. However, he explains in an interview with io9 that the character he's playing would be immensely different from Groot. To read more about the interview, please read the article by io9 here.
Based on Vin Diesel's comments about the role he might play, one can only guess who the Fast and the Furious actor might be playing. However, if you'd like a clue on who he might be playing, I'll just leave this picture here.