Two workers helping build Manchester City's new Etihad Campus were reportedly told to remove their Manchester United shirts.
The pair are thought to have been told that construction firm BAM, who are creating the former Premier League champions' new training facility on Ashton New Road, have a strict no-football shirt policy.
A man, who has chosen to be unnamed, has suggested to the Manchester Evening News that the club may have been "embarrassed" to see workers wearing United shirts while tours around the complex were taking place.
The new training ground is believed to have cost City £120m.