Xavi believes the timing of an international break had an influence on Barcelona's El Clasico loss to Real Madrid in April.
Zinedine Zidane's side snatched victory when Cristiano Ronaldo hit a late winner, despite Sergio Ramos having earlier been sent off, ending Barcelona's 39-match unbeaten run.
Former Barca star Xavi, who now plays for Qatari club Al Sadd, thinks Lionel Messi, Neymar and Luis Suarez travelling to South America for international duty in the build-up to El Clasico had a negative impact on Barcelona.
"From what I understand, the trip to South America affected us a lot," Xavi told the Barcelona website.
"It is not just a player, it was the three up front who made a large journey and then came the Clasico. It affected us.
"If it is another game that you lose 2-1 at home, you could say it would not matter, but El Clasico hurts because it leaves a mark, and it left a mark until the elimination from the Champions League."
Xavi said he believes Barcelona are the best on the planet even though they lost in the quarter-finals of last season's Champions League to La Liga rivals Atletico Madrid.
"This year, Barca were not champions of Europe, but they are the best team in the world by far, without any doubt," the former Spain international said.
"I heard Pep [Guardiola] say this: 'Barca can lose matches but they are the best team'.
"If we did a ranking of the top 10 players in the world, Barca would have five or six. It would be tough to name players for Barca to sign as we practically have the best in each position.
"I have watched at least 95 percent of Barca's matches, as well as other big European teams and I can say, without doubt, that Barca are on another level. They are the best team in the world by far.
"I think the only other team that comes close is Pep's Bayern. But the rest are playing a different sport. I watch Barca and I drool."