The 18-year-old was arrested on Wednesday evening and released without charge later that night.
He was questioned in relation to an alleged St Patrick’s night assault on a 17-year-old from Somerset who was in Dublin for the weekend with some friends.
Guy Wallace, a talented pianist and rugby player, said earlier in the week that his little finger was severed during an incident with five Dublin youths. He believed that they held his finger down on a kerb and then smashed it off by either stamping on it or using a stone, he said.
The finger was never found.
The incident happened after the gang asked him where he was from and he told them he was English, he said.
However, gardaí have since said that the finger did not come off during the assault.
They believe that Mr Wallace may have been headbutted outside a fast-food restaurant on O’Connell Street in Dublin’s city centre. He fled from the scene — CCTV footage shows him running away from the restaurant — and was later found by gardaí on Cumberland Street, attempting to staunch the flow of blood from his hand.
His father, William Wallace, is a Conservative Party councillor in Somerset.
Following surgery at the Mater Hospital on Monday night, the 17-year-old returned to England on Wednesday for further surgery in Plymouth. He is likely to be back in Ireland in the coming weeks to speak to gardaí investigating the case.