Career
In late August 2014, he was loaned to 2. Bundesliga club Union Berlin for the season. His contract with Mainz 05 still runs until 2017.
Queens Park Rangers
On 2 July 2015 it was announced that Queens Park Rangers had signed Polter from FSV Mainz 05 on a three-year-deal for an undisclosed fee.
His full debut came in a League Cup match against Yeovil Town, he scored the first goal for QPR as they secured a comfortable 3–0 victory.