Starting centre Alex Pledger is in doubt for the opening match of the New Zealand Breakers' NBL semifinal series against minor premiers Melbourne United.

Pledger is battling a mystery virus after sitting out the second half of the Breakers' 70-68 road win against the same opponents on Sunday after feeling dizzy at halftime.

He hasn't trained with his teammates in Melbourne today, instead staying back at the hotel.

Assistant coach Judd Flavell says Pledger is awaiting results of tests to determine what the virus is.