As her hour-long set on the Pyramid Stage drew to a close, Winehouse climbed down into the pit to interact with the crowd while she performed her hit song 'Rehab'. It was at this point that she was spotted scuffling with an unseen audience member.
The troubled singer also scolded the crowd after they booed when she mentioned her jailed husband Blake Fielder-Civil.
Amy warned: "Don't boo. I'll find your phone and ring your mum and tell them about your bad manners. Manners cost you nothing."
Some audience members felt that Amy was not yet back on top form, criticising her rambling between songs.
Greg Milsted, 26, told The Telegraph: "I thought her singing voice excellent as always but between songs, the way she led into them seemed a bit confused."
Fellow audience member Laura Bradley added: "It is a shame the crowd didn't appreciate her - they were slagging her off."
Winehouse is expected to check back into the London Clinic today, where she has been receiving treatment. Her father Mitch recently revealed that she is suffering from the early stages of lung condition emphysema.