During the incident, which is said to have taken place at the Berlioz Festival on Tuesday (22 August), Gardiner, 80 allegedly attacked William Thomas, 29, during a performance of the Hector Berlioz opera Les Troyens.
According to The Times, a source from the scene said that no arrangements had been made as to how to enter or exit the stage.
Gardiner allegedly confronted Thomas during a celebration after the show and said: “I feel like throwing this [beer] over your head.
When Thomas warned him to not attempt anything, Gardiner allegedly slapped him in the face followed by a punch.
There was a “brief shouting battle” and then Thomas left the room.
A representative of Gardiner told the Slipped Disc classical music website that Gardiner had been suffering from the “extreme heat”. Temperatures in the French region reached 39C on Tuesday.
The representative also suggested that recent adjustments to Gardiner’s medication “may have provoked a behaviour that he now regrets”.
Another source said that Gardiner felt the show had not gone to plan and it had been “incredibly hot” during the performance.
The classical music website also reported that Gardiner immediately left for London to see his doctor following the outburst.
His Wednesday night’s (23 August) performance was reportedly taken over by his assistant Dinis Sousa.
At this moment, Gardiner is still expected to continue to conduct the Monteverdi Choir in Salzburg, Versailles, Berlin, and the BBC Proms in London.
The Independent has contacted Gardiner’s representatives for comment.
In May this year, Gardiner had been personally chosen by the King to lead the first 20 minutes of music at the coronation.