Keita refused to travel with his teammates after learning that he would not be in the starting line-up in the match against Leverkusen.
Bremen, who suffered a 5-0 defeat in the match, said the 29-year-old Guinean will no longer train with the team or be in the dressing room.
In a statement released Tuesday, Bremen's Head of Professional Football Clemens Fritz said "Naby's behavior is intolerable for us as a club."
"With this action, he has let his team down in a tense sporting and personnel situation and put himself above the team. We cannot allow that," Fritz said.
"At this stage of the season, we (Bremen) need to be fully focused on the upcoming games and have a team that stands very close together. There was therefore no alternative to the measures we took," the Bremen football authority added.
Leverkusen made club and national history after their 5-0 victory. They were crowned Bundesliga champions for the first time in their 120-year-old history. This was also the first time that reigning champions Bayern Munich lost the trophy in at least 12-years.
Bremen, 12th in the Bundesliga standings, are scheduled to host third-placed VfB Stuttgart on Sunday.
Some information for this article was sourced from Reuters.
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