Aaron Wan-Bissaka and Fred were not allowed into the Manchester United changing room after the derby for an hour because they were randomly selected for drug testing.

The pair, who had both played the full 90 minutes, were so dehydrated they were unable to provide a urine sample.

Instead they had to walk the corridors of Old Trafford with a chaperone, according to The Athletic.

Aaron Wan-Bissaka and Fred were unable to provide a urine sample for an hour after the derby

The right-back was dehydrated after keeping Raheem Sterling at bay for 90 minutes

Players are selected at random by the FA to provide samples after matches.

To avoid any potential interference, those selected must provide them before entering their team's changing rooms, and they must be followed at all times by a 'witnessing chaperone' until they produce a 90-mililitre urine sample.

On Sunday, despite the match finishing before 6.30pm, both Fred and Wan-Bissaka did not provide their samples until 7.30pm, according to the report.

It is understood that dehydration from the match was the cause of the delay.

Both players had been randomly selected by the FA to provide samples, as is common practice

Once their samples were taken they could then join their teammates in the changing room.

Both Wan-Bissaka and Fred played major roles in the crucial derby win, United's third victory over City this season in all competitions.

The right-back kept Raheem Sterling quiet all game and provided a threat going forward, while Fred marshalled the midfield superbly.