Uruguay striker Luis Suarez "cannot understand" why players are being forced to play so many fixtures in such a congested period.
South American nations are playing two World Cup qualifiers over the coming days, after FIFA inserted an extra international break into the calendar.
European countries are not in action, but CONMEBOL are attempting to catch up on fixtures missed due to the coronavirus pandemic and last year's Copa America.
Uruguay are one of five teams separated by just two points in the qualification standings, but have lost their past four games by an aggregate of 11-1.
They travel to Paraguay on Thursday, before hosting Venezuela on February 1. However, that second game comes just two days before a crucial Copa del Rey tie for Real Madrid, and Federico Valverde is set to travel back to Spain for that match.
Three other players, Getafe trio Mathias Olivera, Damian Suarez and Mauro Arambarri, could well have to be involved in a LaLiga match on February 4, while Suarez's Atletico Madrid are in action against his former club Barcelona on February 6.
It is a situation that leaves Suarez frustrated.
"I have to speak about the physical part of being a human being as well as a sportsman," he told reporters.
"We cannot understand how it is that we will compete in a World Cup qualifier next Tuesday and that Pajarito [Valverde] in this case, will have to compete in a Copa del Rey match.
"That my colleagues from Getafe, Mauro, Damian and Mati, will have to play that Friday in a LaLiga match. The schedule is quite tight, but we have to adapt to it.
"We are professionals and will do our job on the pitch because that is demanded from us, but sometimes the players are not in other people's thoughts.
"It happened before when we played three qualifiers in 10 days, with long trips of more than 12-15 hours, and obviously fatigue then has an influence."
Suarez, however, insists the squad's full focus is on arresting their dismal form and pushing on to qualify for the World Cup in Qatar this year.
He said: "There are players who go through different stages of both winning and losing streaks. But when you come into the national team, the games that you have been playing suddenly do not matter.
"What matters is the hunger to compete, the wish to live and feel what I feel with this shirt on and to keep demonstrating that I am prevailing and that I want to keep competing and have the burning ambition to make it to the World Cup.
"I've been lucky enough to have played in three World Cups already and now, at 35 years old, I want to continue with that same ambition and I wish to keep playing World Cups and to have the chance to play at my fourth World Cup. Because of that, I am here."