Many people have said to me once you press continue on the first day of your save the game stops mirroring real life. This could be many years in the future and to me £50m seems reasonable if that's what he's going to have to spend to replace the player.
I had a star midfielder for my Luton team valued at £30m. I set the asking price at £75m as that's roughly what I was going to have to spend to get a similar replacement. Arsenal consistently bid £30, and I consistently said no. In the end the player got upset and I had to accept a bid, in the end from United for £45m.
Luton's record transfer free received is nowhere near that, so obviously nothing is realistic, but then it is a game.
The player had 4 years left on his contact with me. Signed for United, had 5 years left and his wagers went from £100k pw to £250k. His value went from £20m to £80m just off that transfer. United play in all the same competitions Luton do (in game, obvs) and only finished 2 points ahead of me last year. Does that really transfer really make him £50m more expensive?