Otis Khan had a release clause of £100,000 contained in his contract with Yeovil Town which was paid by the Stags according to wikipedia.
"In late June, the club received a bid in the region of £100,000 which met the release clause of attacking midfielder Otis Khan from fellow League Two side Mansfield Town, Khan subsequently signed a two-year contract with the Nottinghamshire side"https://en.wikipedia.org/wiki/2017%E2%8 ... .C._season
From Burton Albion forum (May 2018):
"According to TeamTalk, the Brewers are one of four clubs interested in the 22-year-old forward, with Preston North End and League One duo Oxford United and Luton Town also named in the report. Former Sheffield United youth forward Khan scored 10 goals in a superb first half of the 2017-18 season with Yeovil that saw him linked with a January move away from Huish Park. He opted to remain with the Glovers for the rest of the campaign, although he would not score again after December 29 as the second half of his season failed to live up to the early stages. The report suggests Khan has a £100,000 release clause in his contract. Brewers boss Nigel Clough has previously said that "there won't be funds for transfer fees" and Albion are likely to have a quiet summer transfer window if the majority of their current squad stays together, meaning a move for Khan would be unlikely at this stage."