Lions prop arrested after Auckland Test
The 24-year-old was picked up by police at about 03.00 (NZ time) Sunday in the city's Galway Street nightclub area, Fairfax New Zealand reported.
Auckland police did not name Sinckler, but said in a statement that they attended an incident involving "minor disorder" early Sunday.
"A male was placed under arrest but was not charged after further inquiries established that the incident did not warrant prosecution," they said. "He was then taken to his accommodation by police."
Police declined to give further details.
Fairfax, citing a statement from the Lions, reported the Harlequins and England prop had said he was sorry about his behaviour.
"I apologise for putting myself and the Lions in this position and also to the police and anyone else affected," he said.
Radio New Zealand, quoting the same Lions statement, said tour manager John Spencer had addressed the issue with Sinckler and would take no further action.
"I have spoken to Kyle and reminded him of his responsibilities as a Lion, which extend to his off the field behaviour," Spencer said.
"Kyle has apologised for any inconvenience caused and we are satisfied that he regrets this incident and that this is the end of the matter."
Sinckler was on the bench for all three Tests against the All Blacks, including Saturday's 15-15 draw, which resulted in the three-match series ending drawn 1-1 for the first time in history for the Lions in New Zealand.
He was involved in an ugly spat with All Blacks reserve scrumhalf TJ Perenara after the final whistle of the second Test in Wellington.
The tighthead prop reportedly made a comment and refused to walk through a guard of honour formed by the All Blacks after the Lions' 24-21 win.
Earlier in the gruelling six-week tour, Sinckler spoke about his reputation as a hot head, admitting he had let his aggressive streak get the better of him in the past.
AFP have approached the Lions for comment.