The 25-year-old, who missed Euro 2016 with injury, may face the Czech Republic on Saturday and Northern Ireland three days later.
"It is great to be here again. I did not realise it was actually such a long time since my last game. But I know the feeling of a comeback well from the past few years.
"I have not been successful with tournaments. This is not on purpose that I get injured shortly before.
"It was extremely bitter to miss the past two major tournaments. Maybe that is why I want to be healthier and I am not thinking about Russia. I am just happy to be fit again and reach 100%, to stay healthy and enjoy the moment."