The former England manager said: "We could end up winning a treble of Spanish league, Spanish Cup and the European Cup-Winners' Cup, but at the same time we could end up winning nothing."
Robson conceded that his side were favourites to win the Cup-Winners' Cup for an unprecedented fourth time, but said: "Paris St-Germain have not played for 11 days, while we had a very bruising match with Real Madrid on Saturday.
"That game really took a lot out of my players and I think it could have given a big advantage to the French team, who are very well rested."
He said the bomb scare which delayed Barcelona's flight to Rotterdam for four hours on Monday had not unduly disturbed his squad. "They have all got over that and are just looking forward to the match."
Barcelona (probable): Vitor Baia; Sergi, Blanc, Abelardo, Ferrer, Guardiola, Luis Enrique, De La Pena, Stoichkov, Figo, Ronaldo.
Paris St-Germain (probable): Lama; Fournier, N'Gotty, Le Guen, Algerino, Leroy, Cauet, Guerin, Leonardo, Rai, Loko.