Mohamed Zidan scored on his first appearance with Mainz in Saturday’s 1-1 Bundesliga draw with Schalke.
Zidan opened the scoring after 14 minutes but Schalke’s Chinedu Obasi secured a share of spoils 13 minutes after the break.
Dortmunds Zidan joined Mainz on a six-month loan contract until June 2012, with an option for a permanent move until June 2014, while the financial agreement between the two clubs has not been disclosed.