Juventus face the embarrassing prospect of having to play in the Europa League qualifiers in July after defeat to Parma yesterday.
The Bianconeri must now enter Europe through the preliminary round and start their season in late July following a 3-2 home defeat to Parma.
"The team is physically in better shape now, because they have been training regularly for three to four weeks," said Zac.
"It is difficult to keep a side motivated when they are fighting for the Europa League and started the campaign targeting the Scudetto or at least a top three finish.
"It does irritate me, as I confirm that we have not fully expressed our potential. The players are only starting to get better in terms of fitness and so the internationals will be fine for the World Cup."