3 – Gianluigi Donnarumma
The 18-year-old is already establishing himself as one of the best goalkeepers in Europe. He’d be the perfect long-term replacement for De Gea, who himself arrived at United as a young keeper. Donnarumma would not come cheap, but he would be worth investing a huge amount of money in because of the fact he could arguably play for 20 more years! Considering he is already plying his trade at the top level aged just 18, it tells you all you need to know. For me this is the goalkeeper United should be going all out to sign, should De Gea leave.