Panucci limps out of Italy training
Coming just four days after captain and centre-back Fabio Cannavaro was ruled out of the tournament with ankle ligament damage, a second loss to the backline would be a severe blow for the world champions.
Italy were playing a two-touch game in a confined space when Panucci went down all on his own, without any contact from another player.
Italy play their first match on Monday against the Netherlands in Berne.
Italy's director of communications Antonello Valentini said Panucci had felt a pain his knee and left the training session as a precaution.