Man Utd have been left 'red faced' after failing to insert a sell-on clause in their sale of £25m-rated Michael Keane to Burnley.
United officials are reportedly "kicking themselves" after allowing the centre-back, recently called up by England, to leave Old Trafford for Turf Moor in 2015 without ensuring they receive a cut of any future Clarets' profit.
The Sun claim United are apparently embarrassed by the oversight and that "some people are now keeping their heads down".
Leicester City failed with a £15million approach for the Burnley star in the summer and Keane is now being linked with a £25million January move to Chelsea.
The 23-year-old centre-back, who was considered less talented than his twin brother Will by United, is having a superb season in the Premier League and looks certain to leave the Clarets either in January or next summer.