ROB Atkinson is already one of Oxford United's most expensive sales of all time - and the club could gain even more from his move to Bristol City.

The centre back joined the Sky Bet Championship side on Saturday, signing a three-year deal with the option of a further 12 months.

The fee is officially undisclosed, but is understood to be upwards of £1.6million.

It makes Atkinson the 11th player in United's history sold for £1million or more and the seventh since 2016.

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There are various add-ons attached to the 22-year-old's fee which could see the U's gain further financially, though.

United are believed to have inserted an appearance clause in the deal, which nets them cash if Atkinson plays a certain number of games.

The U's also agreed a sell-on clause, so they would earn a slice of the fee if the defender leaves City.

A similar clause was agreed as part of Atkinson’s move to United from Eastleigh in January 2020, in another undisclosed deal.

Neither the U's nor the Vanarama National League club would confirm the details of the sell-on clauses in the two transfers.

Atkinson only made his United debut last September and scored twice in 44 appearances as he helped Karl Robinson's side reach the play-offs.

He is the second player to join City from the U's for a seven-figure sum, after Callum O’Dowda made the same switch five years ago.