Brazilian Football Confederation (CBF) director Juninho has confirmed Brazil will not release Real Madrid players before the end of the international break.
South American teams are in World Cup qualifying action over the coming week, with FIFA having inserted an extra international window into this season's calendar to make up for time lost due to the COVID-19 pandemic.
Brazil has already qualified for this year's World Cup in Qatar and sits top of the CONMEBOL standings on 35 points.
It faces Ecuador on Friday and Paraguay on 2 February.
Madrid, meanwhile, has a Copa del Rey quarter-final against Athletic on 4 February.
Four Madrid players – Casemiro, Eder Militao, Rodrygo and Vinicius Junior – have been called up for Brazil.
However, Juninho insisted that even if the players do not feature in each of Brazil's games, they will remain with the national team until February 2 when the international window ends, meaning there is little chance of Los Blancos having the quartet available for the trip to San Mames.
"We are not going to release the players," Juninho said.
"The players have to be with us until the end of the FIFA period, on February 2. Depending on how they play the first match [we will] discuss whether or not they play the second.
"They will be with us until the end. We are not willing to release them. We cannot set a precedent. We have had requests from other clubs.
"We have a few days with the players. We must take advantage of this year now that the preparation for the World Cup has begun."
Juninho stressed Brazil have turned down Madrid's requests on the grounds of fairness to other teams.
"We can't, it's not that we don't want to," he added.
"In Tite's management it has never happened. That is not the situation, we understand the situation of the clubs. It has happened because of the pandemic. Before, there was no January date. It is the situation that was forced on us.
"We have a very good relationship with the clubs. We always talk cordially. [Brazil coach] Tite has explained the situation to Ancelotti.
"It was in a good tone. They understood our situation and I think they haven't had any problems."
Asked if Tite had discussed the issue with the players in question, Juninho said: "I guess Tite has talked to them and made the situation very clear.
"The October  dates were cancelled and we only have a week to prepare for the World Cup [in November]. There is only one week for Tite to be with the players and see how they are. The clubs understand that.
"I also spoke with [Paris Saint-Germain director] Leonardo and the English clubs on other occasions with the same problems."