Ok, let's do the maths
38 games in the league, then let's say 6 CL games plus 6 EL games (don't see you in the final next year, no offense), 4 League Cup and 4 FA Cup games, is 58 games. Let's say for argument's sake he's subbed in each game.
Training sessions, let's say 5 a week for 48 weeks, it's 240.
"Ref at the weekend"? Whatever, another 58 games?
(58*300)+(240*5)+(58*5) = 18.890 €
Man United are offering him 8m € net per year
8.000.000€ - 18.890€ = 7.981.110 €
He would have 7.981.110€ left. You're a regular Adam Riese, aren't you.