The all-rounder, due to fly out to India this week to play in the IPL, suffered severe head injuries after an incident in Merivale.
New Zealand cricketer Jesse Ryder in coma after being attacked
But he is in a medically induced coma after suffering severe head injuries as a result of the incident in Merivale last night.
A statement on the New Zealand Police website read: "Police are investigating an incident at a bar in Merivale in the early hours of this morning.
"Police can confirm the incident did involve Jesse Ryder and that he is currently in Christchurch Hospital."
He was involved in an altercation with up to three people outside the bar, one of whom followed him to a car park nearby and assaulted him.
He had been drinking with Wellington team-mates after playing for the Firebirds in the major preliminary final against Canterbury Wizards at Hagley Oval earlier in the day.
Ryder, a controversial figure whose career has been plagued by off-field incidents, is on an indefinite break from international cricket and has not played for New Zealand since February last year.
Ryder has played 18 Tests and 39 one-day internationals for the Black Caps, his last appearance an ODI against South Africa.
New Zealand Cricket posted a message of support for the all-rounder on Twitter, saying: "The whole NZC team's thoughts are with @DijaRyder this morning."
David White, New Zealand Cricket's chief executive, Peter Clinton from Cricket Wellington, Heath Mills from the New Zealand Cricket Players' Association and Ryder's manager Aaron Klee were flying to Christchurch.
"We are all shocked by what has occurred and extremely concerned for Jesse. New Zealand Cricket's thoughts are with him and his family", White said.
Follow us @SprtNationalUAE