The injury-hit holders, who will be without striker Patrick Kluivert, have an uphill task after losing the first leg 1-0, and van Gaal thinks his team have only "a 30 per cent chance of getting through". But he added: "Greek fans consider Panathinaikos players as heroes after their win in Amsterdam [in the first leg]. They want them to reach the final at any cost and this will make them very nervous. We must take advantage of any mistakes."
Some 80,000 fans are expected at Athens' Olympic stadium as Panathinaikos seek a place in the European Cup final for the first time in since 1971, when they were beaten 2-0 by Ajax at Wembley.
Panathinaikos, back on top of the Greek league after a 1-0 Athens derby win over AEK, are confident but do not underestimate their task in earning a tilt at either Nantes or Juventus. Their Argentinian coach, Juan Ramon Rocha, said: "I want all Greeks to help us. It will not be easy to reach the final because Ajax will attack like hungry wolves from the first minute.
"The first leg win gives us an advantage but anything can happen. I said before the first leg that Ajax is the best team in the world and we respect them. But the respect ends when the match starts."
Much of Panathinaikos' hopes in front of goal will again depend on the mercurial Polish international striker Krzysztof Warzycha, who scored in Amsterdam, his sixth goal in the European campaign.
Nantes will be seeking inspiration from Bordeaux as they attempt to overcome a two-goal deficit against Juventus. Few gave Bordeaux much hope of beating Milan in the Uefa Cup quarter-finals after losing the first leg 2-0, but they produced a stunning 3-0 victory.
French teams have thrown away their traditional complex against Italian sides this season, with Paris St-Germain beating Parma in the European Cup-winners' Cup' and Lyon removing Lazio from the Uefa Cup.
Nantes, who have never reached a European final, know they have a tall order against Juventus, even if the Italians did lose 3-0 at home to Sampdoria on Saturday.
Juventus, European champions in 1985 and losing finalists in 1973 and 1983, have their French midfielder Didier Deschamps back from suspension to play at Nantes' Beaujoire stadium, where he started his career in Nantes.
Marcello Lippi, the Juventus coach, sounded only mildly confident of the outcome. "I would rather be in our position than that of Ajax. But the tie is not over, especially as Nantes will have two important players back in N'Doram and Makelele."
In fact, the Chad midfielder Japhet N'Doram faces a fitness test.Reuse content