I would suggest that it is fairly certain that Unai Emery will go with Nicholas Pepe and Pierre-Emerick Aubameyang up-front against Man Utd but who will the Spaniard pick as the third man, either on the wing or just behind?
Since Lacazette got injured it was thought that Reiss Nelson would slip into his role, albeit in a different position up front but both Bukayo Saka and Gabriel Martinelli have also staked a claim and there is always the chance that it could be Mesut Ozil.
Obviously, it depends on which formation Emery goes with and that in itself is difficult to second guess but there are indications as to what the manager will do depending on the formation.
If he goes 4-3-3 then I reckon he will slip Saka in on the left with Auba down the middle and Pepe on the right side, however, if he goes say 4-3-1-2 then I can actually see him playing Ozil just behind Pepe and Aubameyang,
Looking at the different options I do not see where Emery will fit in Martinelli simply because Auba has the middle role and the young Brazilian has not struck me as a sort of winger. Nelson could fill that role but I believe that Saka has moved ahead of him in the managers thinking.
It is all guesswork at this stage but as an educated guess I am fairly confident that if Emery goes with a three-man front line it will be Saka, Aubameyang and Pepe, if he goes with two forwards and one just behind then it will be Ozil behind the front two.