What's the reason as to why Arsenal have to break even in transfers this year? I have no clue about Arsenals financial situation.
It's not true. Arsenal don't have to sell Sanchez to be financially stable.
There's a limit on wage increases year on year, and if you want to increase your wage bill by more than that you have to make up for it with incoming money, either commercially (Not going to happen at short notice) or through player sales. There's a good article on it here -
http://www.independent.co.uk/sport/...sanchez-mesut-ozil-new-contract-a7803741.html
Arsenal mouthpiece Ornstein has suggested it'll need to be a net spend of 0 to afford the 2 salary increases.