Roman Burki questioned where his team-mates' desire was after Borussia Dortmund were thumped 4-0 by Hoffenheim on the final day of the Bundesliga season.
Dortmund's 2019-20 campaign ended on a deflating note as they crashed to a second successive home defeat thanks to four goals from Andrej Kramaric - all of which came in the opening 50 minutes.
Lucien Favre's side had little to play for given it was already confirmed they would finish second and they were blown away by a Hoffenheim side that moved up to sixth and qualified for the Europa League group phase next term.
Burki suggested it was evident there was a sense of apathy from BVB from the opening 45 minutes, when Kramaric scored two of his four goals.
"Already after the first 45 minutes you noticed that there was a team on the pitch that wanted it - and a team that didn't feel like it," he said to Sky.
"That shouldn't be. It's a Bundesliga game. We should all be happy that we can play here. A lot of things were wrong and then the result is."
Dortmund were only four points adrift of Bayern Munich when the Bundesliga resumed last month and an impressive 4-0 victory over Schalke first up indicated they were ready to run their great rivals close.
However, the final gap between the two clubs was 13 points as Dortmund tailed off and Bayern secured an eighth successive title having won all of their nine games after the coronavirus-enforced break.
Burki, who has been with Dortmund since 2015, admitted BVB must match Bayern's approach if they are to dethrone them next time.
"We have to keep working on this winning mentality," he added.
"Bayern have more than we do, and in the end you will miss the points from the smaller games.
"I have not won against Bayern many times and I can only explain that by not having the right attitude or mentality."