The Copa Libertadores champions are currently unable to maintain match fitness because Brazil's domestic season finished on Sunday, Renato said, reports Xinhua news agency.
In addition, midfielder Cristian and attacker Cicero will not travel with the team due to tournament rules that bar the participation of players contracted after August.
"Other teams are going to have an advantage. They are playing. By the time our first game comes along we'll have not played for 15 days. It's going to be difficult," Renato told reporters on Tuesday.
"I don't understand the decision by FIFA to disallow Cristian and Cicero. The competition is going to be weaker in their absence, but Gremio will suffer most."
Gremio will also be forced to travel in two groups due to the lack of availability on commercial flights from Brazil to the United Arab Emirates.
The club only secured a place in the competition last week when they defeated Argentina's Lanus in the Copa Libertadores final.
In addition to Cristian and Cicero, Barcelona target Arthur will also be missing from Gremio's squad for the tournament due to an ankle injury.
Gremio will make their debut in the tournament against either Pachuca of Mexico or Moroccan outfit Wydad Casablanca in Al-Ain on December 12.
The winner will earn the right to play in the final at the Zayed Sports City stadium in Abu Dhabi on December 16.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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