Ryder, one of the most gifted batsmen in New Zealand, was in Christchurch playing for Wellington against Canterbury in the semi-final of the domestic one-day competition on Wednesday.
Many leading cricketers used Twitter to express their shock and concern for Ryder.
The New Zealand team's official Twitter page said ''The whole NZC team's thoughts are with (Jesse) this morning.''
West Indies star Chris Gayle posted in a Twitter message: ''Will have Jesse in my prayer. Pray for Jesse. Let's hope he gets better soon.''
Former England captain Michael Vaughan tweeted: ''Devastating news regarding Jesse Ryder. Just hope he can pull through. Thoughts are with him and his family.''
Australian pace legend Glenn McGrath tweeted: "Our thoughts are with NZ cricketer Jesse Ryder & his family. Jesse was assaulted & is in intensive care. We wish him a speedy & full recovery."
Ryder was due to leave New Zealand on Friday to take up a $260,000 contract with the Delhi Daredevils in the Indian Premier League. He has played 18 tests for New Zealand, scoring three centuries and six half centuries with a top score of 201 against India.