The buy-back clause is now a regular feature in the contracts of young players who are sold.
When negotiating, the selling club agree a fee with the buying club for which they can bring them back down the line.
One team gets their man and the other guards themselves against being stung in the future, if that player fulfils their potential.
But why have we seen a recent rise in buy-back clauses and 'matching rights'?
Which players have buy-back clauses?
Chelsea have the option to buy Tammy Abraham back from AS Roma for £68m
The buy-back clause is not a completely new phenomenon and there have been high-profile instances in recent years.