No, for sure he hasn't lost it. Zidane is a legend who can pass the dip in form he had. I am sure he'll prove in EURO 2004. It wasn't just him who had a low performance in El Real. Becks, Carlos.... Big names that suffered of that long, full of pressure season.
Zidane, like almost all the team, did a good job at the first half of the season but things turned around for the few last matches.
With less pressure, better line-up and high spirit Zizou will back to the top again, I am sure.