He left north London in 2014 after nine years to join Wolfsburg, but now he is back.
The former Gunners striker signed a two-year deal with Nottingham Forest last month, as he looks change his reputation and prove his ability in England.
The 28-year-old uploaded a post to his Instagram profile, ahead of the third-round clash with his old employers at the City Ground.
The Danish star juggled the ball (in his underpants!