The actor was fighting Sir Kenneth in the cursed play when he was hit with one of the real swords which are used for the battle scenes, audience members said.
He was checked over by on-site medics and continued with the performance, but after the curtain dropped he was taken to hospital to be checked over.
A spokeswoman for the Manchester International Festival said that they are unable to confirm the rumour that the unnamed actor was injured with Sir Kenneth’s sword due to the number of cast involved in the scenes.
The injured man was not one of the "big stars" in the acclaimed adaptation of Shakespeare’s play, she added.
Sir Kenneth, who co-directs and stars in the production in a deconsecrated church, has admitted that it is not the dramatic battle scenes in the play are risky.
“There is enormous concentration,” he told BBC Radio 4’s Today programme. “It is impossible to say that it is without danger. Metal clashes, sparks literally fly.”