Mexico go into the Confederations Cup with an 18-match unbeaten record but with their preparations hit by controversy after the withdrawal of striker Cuauhtemoc Blanco and the possible release of five players due to club commitments.
Blanco pulled out of the squad one day after leading his club America to the domestic title at the end of May, saying he was tired.
Guadalajara, who have had five players selected, have asked for them to be released to play in the Libertadores Cup, which clashes with the tournament in Germany.
The team known as the Chivas have reached the quarter-finals of the Libertadores, the South American equivalent of the Champions League, in which Mexican clubs take part as guests.
Coach Ricardo La Volpe has been criticised for his handling of the situation. Critics say he accepted Blanco's decision to withdraw from the squad but wants the Guadalajara contingent to stay.
The gruff Argentine coach hit back, denying that the fiery Blanco had been given special treatment.
"The mistake that all the journalists and the president of Chivas [Jorge Vergara] have made is that I didn't give any special permission to Cuauhtemoc Blanco," La Volpe said.
"He was on the list, he said he was tired and I replaced him with someone else, I didn't give any special permission for anyone."
When Vergara said the federation should release his players, La Volpe retorted: "If the Chivas players prefer to play in the Libertadores, they can tell me and I'll take them off the list."
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Guadalajara midfielder Ramon Morales said he had been caught in a tug-of-war.
"Both the Chivas and Mexico are just as important for me," he said. "I feel like I'm between the wall and the sword."
La Volpe had been hoping to take a full-strength squad to the Confederations Cup, a welcome chance for his side to test themselves outside their region.
Mexico have not lost a game since they crashed 4-0 to Brazil at the Copa America quarter-finals in Peru last July.
However, although their run is impressive, most of their games have been either World Cup qualifiers against modest opposition from the Caribbean and Central America or friendlies against second-string European teams played in the United States.
Their unbeaten run does not include any wins against major footballing powers and La Volpe is eager to test his side against the world and European champions, Brazil and Greece, who are both in Mexico's first-round group.
"It's a great tournament and we want to take the best possible team," said La Volpe in a recent interview with FIFA's website. "We have an obligation to do well.
"It will give us an idea of what we will find in 2006 and allow us to compare ourselves against teams of high potential."
Mexico staged and won the 1999 Confederations Cup, beating Brazil in the final, and will be making their fourth appearance in the competition.
They kick off against Japan in Hanover on Thursday before playing Brazil in Hanover three days later and Greece in Frankfurt on June 22.
