Mats Hummels' unwillingness to compete for his spot at Bayern Munich led to his Borussia Dortmund return, according to Niko Kovac.
Hummels, 30, returned to Dortmund for a reported €38million last month, ending a three-year stay at Bayern.
Bayern had already agreed a reported €80m move for Atletico Madrid and France defender Lucas Hernandez, who they intend to use at centre-back.
With Niklas Sule already part of the Bundesliga champions' squad, Kovac said Hummels had no interest in fighting for his place at Bayern.
"Mats did a great job, especially in the second half of the season," the Bayern head coach said on Tuesday.
"Like [Bayern president] Uli Hoeness said, at the end of the season Mats came to us and asked what the status quo was for the new season.
"Niklas Sule did a great job, he is a starter of the [Germany] national team and with Lucas we bought a player that we want to play centre-back. That doesn't mean anything.
"Competition means the best player will play. In that case, Mats wanted to avoid that. We accept that and the result is that he plays for BVB now."
Hummels won three Bundesliga titles and a DFB-Pokal during his second stint at Bayern Munich.