You won't.
Take this example, the one star that I'm still trying to sell:
You see it all well until you realize he has a 6.6m upkeep, which means you need to pay 235.7k a day to keep him. A week later you lose 1.65m.
I'm sure you would go bankrupt in less than 2 weeks if you try to keep this one player in your club as a level 4.
But sure he would be a nice 5* for a level 17 player that could afford him...