Ryder was attacked by two or three people when he was leaving Aikman's Bar in the suburb of Merivale late last night and it appears that the cricketer had been assaulted twice, Christchurch Police said.
The 28-year-old is in intensive care unit with a fractured skull and is in an induced coma due to multiple injuries.
The first attack took place outside the bar where Ryder was out with his Wellington teammates after their team suffered a semifinal loss in the domestic one-day competition here earlier in the day.
In a statement, New Zealand Cricket (NZC) has expressed grief over Ryder's serious condition.
"We are all shocked by what has occurred and extremely concerned for Jesse. New Zealand Cricket's thoughts are with him and his family," NZC chief executive David White said.
The New Zealand Players Association (NZPA) too were in shock over the assault.