United kickoff their Champions League campaign at Old Trafford against Bayer.
"They will be a tough test, that's for sure," Giggs told United Review. "German football is on a real high at the moment and last season's final, with two German teams at Wembley, proves that.
"Bayern Munich have been terrific for a long time now and then the emergence of Dortmund has been really exciting. They play the game with so much energy and make life really difficult for you. A lot of people were blown away by them last season.
"At the moment, Germany has a lot of good young players coming through and a good national team that's not only getting results but performing well and playing attractive football."
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