Sunderland can sign Trabzonspor fullback Ondrej Celustka for £2.5 million.
Celustka has impressed in the opening games of the season on-loan from the Turkish club.
As is this the case with all overseas loans, a clause has been built into the deal to convert it into a permanent switch, says the Sunderland Echo.
But Sunderland would have to pay a fee of £2.5m to activate that agreement next summer, if they want to keep the 24-year-old.
For the big stories and the banter follow us on Twitter: @tribalfootball