The former Liverpool midfielder has been suspended to the end of the season after refusing to travel with the squad to Bayer Leverkusen last week.
Fritz said: "He is here, training individually. For us, it is now simply a matter of calming down and focusing on the essentials.
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"He has apologised, shown understanding - and we believed him. Nevertheless, it was difficult for us and we had to show a certain degree of consistency. And that is what we did."
On Keita's future, he added: "My job is to concentrate on the next games. We'll see what happens from the summer onwards."