Johnson is Cardiff's sixth signing of the close season

The Swans had a �100,000 offer rejected last month for the defender, and were preparing to return with a higher bid.

But Cardiff have beaten them to the punch by agreeing a �275,000 deal with Wycombe for the centre back.

Johnson, 23, has spent all of his career so far with Wycombe, starting almost 150 league games for the club.

Cardiff say they will pay the transfer fee in instalments, and a small future sell-on clause.