Mane ended his six-year stay at Anfield to embark on a new challenge with Bayern, who have won the last ten Bundesligas.
Winning is in the DNA of the German side, however, Saunders couldn't get his head round why Mane left Liverpool for the Bavarians.
Shortly before the £35million move was completed, Saunders told talkSPORT: "Nothing against the club, it's a great club, but the league is nowhere near a challenge for Mane.
"He'll get goals. They win 5-0 every week, only one team can win the league.
"It's not a challenge. He will get in his armchair, light a cigar up, he'll play for Bayern in third gear and he'll coast for two years and ruin the best two years of his life as a footballer.
"At the end of his career, if he said to you: 'come and look at my trophy cabinet', the German league winners medal will be right at the back."
Saunders added: "I can't get my head round why you'd want to leave Liverpool right now, when you're playing the best football of your life in the best combination front-three he'll ever play in, to go and play for Bayern Munich."
Many may agree with ex-Liverpool striker Saunders, however, Borussia Dortmund CEO Hans-Joachim Watzke is definitely not in that camp.
Watzke has been quoted by BILD responding: "There are always some arrogant idiots like this one.
"As a member of the board of Europe's Club Association, ECA, I know that German football still has a good reputation.
"The English didn't win any of the three European Cup titles in the past season."