Leeds United have been fined £2,000 after they included six loan players in their squad for the game at Burnley on 28 November.
Football League rules stipulate that only five on-loan players are allowed to feature on the match-day team sheet.
The Football League heard that Leeds had to contend with a last-minute injury to defender Matthew Kilgallon.
The Championship strugglers, managed by Dennis Wise, have had £1,000 of the fine suspended.
Graham Stack, Matt Heath, Ugo Ehiogu, Tresor Kandol and Geoff Horsfield all played as Leeds lost the game 2-1, while Tony Warner was an unused substitute.