Ex Liverpool and Manchester City star Dietmar Hamann reckons Borussia Dortmund only beat a Celtic team who play in "third rate" Scottish football.
It comes after the Bundesliga giants slumped to defeat against Union Berlin just days after crushing Brendan Rodgers' side in the Champions League.
And 59-time capped ex-Germany midfielder Hamann reckons Dortmund's romp against the Hoops didn't count for much as he took a swipe a the standard of the Scottish Premiership.
He said: "If you score seven goals against Celtic, you have to be aware they play in Scotland, which is second or third rate football.
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