The Leicester Tigers centre, who pleaded guilty, was suspended from May 19 to June 22 by an RFU disciplinary panel of disciplinary officer Judge Jeff Blackett, Philip Evans and Jeremy Summers.
Tuilagi can play again on June 23. He was also ordered to pay £500 in costs.
Blackett said: "This was a top-end entry offence because there were three punches, the third of which was extremely forceful and caused significant injury. However, we also determined that there was some provocation from Chris Ashton who pushed and struck him in the back with his knee.
"The Top End range is 8-52 weeks and we determined that the appropriate entry point within that range is 10 weeks. This was reduced by 50 per cent to reflect Manu’s youth and inexperience, his admission of guilt and his genuine remorse.”
Blackett added: "This sort of incident is very damaging to the image of the game and there is no place for this type of offending on the rugby pitch. Nevertheless we are confident that Manu Tuilagi will learn a valuable lesson from this.”