[2] Hennings has previously played for Hamburger SV, VfL Osnabrück, FC St. Pauli, and Karlsruher SC in the Bundesliga, 2.

Hennings started his career with local junior side VfL Oldesloe before signing for Hamburger SV in 2001.

[6] He again struggled for goals, only scoring twice in 21 appearances[9] as the side finished in 8th position, however, St. Pauli made the move permanent at the end of the season in July 2009 for €200,000.

[8] He spent three years at St. Pauli as a permanent player winning promotion to the Bundesliga in the 2009–10 season as the side finished runners-up in the 2.

Bundesliga, Hennings struggled to break into the first team, making only seven appearances,[12] and in January 2012 he was sent out on loan to former club VfL Osnabrück in the 3.

[6] Karlsruher SC made a good return to the second division finishing in 5th place as Hennings scored 10 goals in 31 appearances.

[14] Despite having made regular substitute appearances during Burnley's Championship-winning campaign in 2015–16, he did not feature in the Premier League the following season.

He gained five caps at this level scoring twice in a 3–2 victory over Greece as Germany failed to qualify for the main tournament.

[20] He featured heavily in the qualification for the 2009 UEFA European Under-21 Championship, finishing as joint top scorer in the qualifiers with seven goals.