Jockey Nathan Berry is being treated in a Singapore hospital for suspected viral encephalitis after collapsing during trackwork at Kranji.

Berry was due to make a flying visit to Sydney to ride Golden Slipper contender Unencumbered in the Todman Stakes at Saturday's Rosehill meeting but his twin brother Tommy will now step in.

A rider has yet to be found for White Sage in the Coolmore Classic.

The 23-year-old Australian rider was at the canteen taking a break between two rides on Tuesday when he collapsed.

Berry, who began a four-month contract in Singapore on March 1, rode a winning double on Sunday.

His Australian manager Ryan Roberts said he was expected to remain in hospital for 48 hours.

Tommy Berry said on Twitter on Tuesday evening his brother was doing OK.

Viral encephalitis causes inflammation of the brain and early symptoms are similar to the flu or other viruses.