Arsenal agreed a special sell-on clause ahead of signing Kieran Tierney from Celtic.
The Scottish international's move was confirmed yesterday with the Gunners splashing a record-breaking 25million on the 22-year-old left-back.
The Sun says Arsenal chiefs had to go to extreme lengths to get the deal over the line, with their Bhoys counterparts playing hard ball over Tierney's move throughout the summer.
The Gunners had seen two bids rejected by the Scottish champions before they eventually met their asking price.
And the North Londoners had to also agree to Celtic's sell-on clause demands - reportedly worth up to 15 per cent of the left-back's potential sale in the future.
