Schmitz explained that her absence from the Nurburgring Endurance Series race was due to her health issues, opening up in a post on social media.
She wrote: “Dear friends of professional motor sport. Many of you have probably wondered why I was on the list of participants on our Porsche in the NSL and then didn’t drive after all.
“I would like to provide enlightenment here, I think I owe it to my/our fans!
“Since the end of 2017, I have been fighting an extremely persistent cancer that has not been eliminated with the resources so far. It got a little better – but now it’s come back with full force.
“Now I have to draw all the strength and nerve to master the next powerful therapies … hoping something [good] will happen. So I say goodbye ‘probably’ for the first time this season.
“In addition, I would like to thank everyone for their help and support in my everyday life, and encouragement in writing! So sweethearts, now you have an update. Please stay healthy and cheerful, see you at the ‘Ring.”