The 23-year-old, who has not managed a minute of competitive action since suffering nerve damage in his back in Germany's with Paraguay on 14 August 2013, says he now plans to "use the summer months" to get his fitness back up to the necessary standard.
"I'm feeling a lot better now and am only focussing on the future," Gündogan told SportBild. "I've seen various specialists and even sought expert opinion in Ukraine. My cousin plays international volleyball for Turkey. She had the same injury a couple of years ago and received successful treatment over there. My goal of being fit for the start of BVB's season is realistic."
The former 1. FC Nürnberg midfielder, who will also miss out on the FIFA World Cup due to his injury, has scored 12 goals in 104 Bundesliga appearances all told, but hasn't featured in the top flight since helping Dortmund to a 4-0 win over FC Augsburg on the opening day of the 2013/14 campaign.