Vincent Kompany is facing his biggest challenge yet in his short stint as Bayern Munich coach. He says it’s time to learn.

Kompany’s Bayern was comprehensively outplayed in the 4-1 loss to Barcelona on Wednesday as Raphinha picked holes in the backline to score a hat trick. Kompany tried to respond with a quadruple substitution in the second half, but it had little impact.

Kompany told broadcaster DAZN that there could be “no excuses” and emphasized unity at a club which was notorious for its locker-room drama under his predecessors. “We will of course stick together and learn from this game,” he said.

It was part of a broader slump by German clubs in the Champions League this week. Borussia Dortmund gave up a 2-0 lead in its 5-2 loss at Real Madrid, while Leipzig’s loss to Liverpool left it with no points so far.

Bayer Leverkusen seemed to have one eye on its Bundesliga title defense after making eight changes in a 1-1 draw at Brest, while Stuttgart was the only team with much to celebrate after beating Juventus.

For Bayern, at least, the signs had been there earlier. Even after the high point of a 9-2 demolition of Dinamo Zagreb last month, Harry Kane warned Bayern had a tendency to lose focus and “against the top opposition we could get punished for that.” So it proved.

“We had a spell in the first half when we looked really dangerous, but Barcelona played well, and we didn’t exploit the time when we were better. Then we got punished in transitions,” Kane said this week.

“We have to go away and learn from this. There was a moment for us when we looked dangerous, but perhaps we got a bit carried away trying to play the final ball too quickly.” Bayern remains top of the Bundesliga but has one win from its last five games in all competitions — though that was by an impressive 4-0 over Stuttgart last week. Kompany’s team will be expected to win on Sunday against Bochum, which is without a win and has two coaches sharing the top job after Peter Zeidler was fired last week.

Still, Bochum’s loud, compact, old-fashioned stadium can be a tricky place to visit, as Bayern found out in a 3-2 loss there in February.

Dortmund’s road woes 

Dortmund coach Nuri Sahin’s approach is under scrutiny, too.

The loss at Real Madrid on Tuesday — after leading 2-0 — not only raised questions about Sahin’s tactical approach, but also continued a worrying trend away from home.

Consecutive away losses to Madrid, Union Berlin and Stuttgart have seen Dortmund concede a total of 12 goals, even as Dortmund kept up a perfect record of five wins from five at home under Sahin. Saturday’s trip to Augsburg in the Bundesliga is a chance for a valuable away win.

One tactical switch brought particular criticism. When Sahin took off attacking midfielder Jamie Gittens, scorer of Dortmund’s second goal, for defender Waldemar Anton in the 55th minute, Dortmund was leading Madrid 2-0. Seven minutes after that, it was 2-2.

“If you lose and concede five goals,” Sahin said, “you can obviously say that the change of system was incorrect.”