Hooper seemed eager to claim a hat-trick, and he flashed a volley just wide of the mark after a cut-back from right-back Cha Du Ri.
Du-Ri, who was with Freiburg last season, also spent spells at Eintracht Frankfurt, Mainz and Koblenz.
Du-Ri has previously played for Bayer Leverkusen, Arminia Bielefeld, Eintracht Frankfurt and Mainz.
And Munich made sure of the three points when Freiburg's South Korean defender Du-Ri Cha scored an own goal.
Lennon said he had been watching Du-Ri for a while and has added him to the club alongside left-back Charlie Mulgrew.
The striker then headed into the path of Koo Ja-cheol following a cross by Cha Du-ri, and his forward partner doubled the lead.
Lennon has released midfielders Zheng Zhi and Koki Mizuno, but has added defenders Charlie Mulgrew and Cha Du-Ri as he seeks to rebuild the squad.
Shaun Maloney was expected to return to the Celtic midfield, but was replaced at the last minute by Cha Du-Ri after complaining of feeling unwell.
Celtic's new signing from Cardiff City, Joe Ledley, started in midfield, while South Korea international Cha Du-Ri, signed after he left Freiburg, came on as a substitute.
And in the sixth minute Cha Du-Ri, playing in a more advanced role on the right of midfield, failed to connect with a superb Emilio Izaguirre cross from the left.
Glenn Loovens and Cha Du-Ri were dropped from Celtic's starting line-up, with Thomas Rogne and Mark Wilson stepping in, although Cha did start after Shaun Maloney was a late withdrawal.
Nicknamed "The Human Weapon", Du-Ri also played in the 2002 World Cup, but as a forward, and has since converted to defence and is now noted for his willingness to join attacks.
Brown had returned to the Celtic midfield in place of Ki Sung-Yeung, while Charlie Mulgrew, Shaun Maloney and Cha Du-Ri came in for Mark Wilson, Georgios Samaras and the injured Emilio Izaguirre.
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