Legendary German hero Toni Kroos has branded Celtic as 'second class opponents' as he slammed Borussia Dortmund despite their recent Champions League romp.

Celtic were sent crashing back to earth in their second round of fixtures in the competition when they were crushed 7-1 by the Bundesliga cracks, after hammering Slovan Bratislava in the first game 5-1 at Parkhead.

Kroos retired after the summer's European Championships where he helped his country to a 5-1 win against Scotland in the opening game of the tournament.

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And the 34-year-old former Real Madrid midfielder - who is the most decorated German player of all time having won 34 trophies in his 17-year career - took a swipe at Celtic while discussing Dortmund's poor domestic start to the season on his podcast he co-hosts with his brother Felix.

He said: "I think the last week was the classic example of a Borussia Dortmund week.

"They won 7-1 in the Champions League - even if it has to be said that it was against a second-class opponent.

"And then they went to play a Bundesliga game at the weekend and put in a typically poor performance and lost.

"In the end, Dortmund will be judged by how they do in the Bundesliga, not in Europe.

"They won't make it to the Champions League Final every year. They have to finally show some consistency in the league.

"I think we can say that Dortmund should be doing better in the league for many years now."