According to the local media, Ryder suffered lung damage and skull fracture and is currently in critical condition in the Christchurch hospital.
Detective Senior Sergeant Brian Archer said at the nationally televised news conference: "Jesse was taken to hospital where he remains in intensive care in a critical condition in an induced coma after suffering multiple injuries".
Four men, believed to be in their late 20s, allegedly started hitting Ryder in the bar's outdoor courtyard and the fight was pushed out on to the road.
"Four dudes were just laying into him and absolutely smashing him on the ground," said a witness who had been in the bar. "His shirt was ripped off and they were kicking him and punching him while he was down".
Ryder managed to stand up during the attack but was quickly knocked back to the ground, the witness added, and they "damn knew who he was". The attackers were reportedly swearing at Ryder as they beat him and ran off when police sirens were heard.
Ryder's career has been blighted by off-field incidents, usually involving alcohol, though he appeared to be in a stable mindset this summer where he played consistently well for the Firebirds.
Last year, he and team-mate Doug Bracewell were reprimanded by Black Caps team management for "unacceptable behaviour" after the pair "verbally reacted to taunts from a member of the public" outside a Napier bar.
Ryder has been dropped from the Black Caps side multiple times, and in 2010 revealed his own troubled history with alcohol.
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