European kings Barca face Asian champions Al Sadd in the semi-finals on Thursday after a pulsating 3-1 'Clasico' win at Real Madrid last weekend.
Mascherano told reporters on Tuesday that the long flight and quick turnaround were tough and Barcelona would not underestimate their Middle Eastern opponents.
"It's difficult to sleep well," the former Liverpool enforcer said after training in Yokohama, the bags under his eyes testifying to his problems.
"We are trying to adapt with (sleeping) tablets but it's difficult," added the Argentine. "We know the team from Qatar is very physical. They're strong and have had more time to prepare.
"We played on Saturday and arrived (in Japan) after the game, 13 hours flying. It's not easy to beat a team like (Al Sadd) in this kind of a tournament."
Before training, Mascherano, Lionel Messi and the Barcelona squad presented personalised replica shirts to a group of children from Fukushima, the area north of Tokyo hit by a nuclear meltdown triggered by March's deadly tsunami.
"It was nice to be able to do that for the kids," said Mascherano. "We will try to put on a special performance for them on Thursday."
Mascherano said Saturday's win, which pushed the Spanish champions above their fierce rivals at the top of La Liga, had given them an energy boost ahead of their Far East trip.
"It could be a plus," he said, scratching the stubble on his chin. "It was an important win but we have to forget that game and focus on this tournament. It's really important to win this trophy."
Barcelona will be bidding to win the seven-team Club World Cup for the second time in three years after beating Argentina's Estudiantes in the 2009 final in Abu Dhabi.
"We will do everything to win the trophy because it will mean we are the best team in the world," said Mascherano, twice an Olympic gold medal winner.
Al Sadd beat Tunisia's Esperance 2-1 in the quarter-finals at the weekend to earn a crack at Barcelona, who are expected to face Brazil's Santos in Sunday's final in Yokohama.
Santos, who were crowned South American champions for the third time in June, almost 50 years after Pele inspired them to back-to-back titles in 1962 and 1963, face J-League champions Kashiwa Reysol in Toyota on Wednesday.
"Everyone (else) is thinking about Santos," said Barca defender Gerard Pique, looking more refreshed than Mascherano after a sightseeing trip to Tokyo and a sushi lunch.
"First we have to qualify for the final. But definitely beating Real Madrid has made it much easier. If we lost that game it would be really difficult to fly here.
"It's really important to win the Club World Cup. A lot of people say we're playing the best football or are the best team in the world.
"But you have to show why and win these titles. They will remember you in history, 20 years from now, for the titles, not how you play. If you don't win people won't remember.
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