Green finished 18th and last in the DTM standings, scoring just 27 points, with nearest driver and Audi stableman Loic Duval scoring twice as many points in 17th.

Between 2015-17 Green finished in the top three of the championship standings, but he struggled to find a balance that worked for him in 2018.

Audi also struggled after losing its aerodynamic advantage under the simplified aerokit rules for 2018, with only Rene Rast able to compete for the title against the dominant Mercedes.

Green's best result in 2018 was fifth in the Red Bull Ring's first race.

"This quite obviously was the worst DTM season in my career. I finished last and it was the first time I did so," he told DTM.com.

"We had major problems in the first three or four race meetings. And my engineer and I in particular didn't make major progress regarding the setup of the car as we couldn't go testing.

"We never got the things really sorted out. Only in the closing stages things got better – but then, the season was over.

"Some of our guys got it right, particularly Rene. But the other Audi drivers also had to cope with ups and downs.

"And the other manufacturers lacked consistency as well."

When asked for the full reasons for his struggles, Green added: "From a certain point in time, it isn't important for Audi to get me from 18th to 10th place in the championship.

"Now they focus on something else. The goal was to support Rene in his championship campaign.

"In the closing stages of the season I was at the very end of their priority list. Particularly on the final race weekend, at Hockenheim, I tried to help Rene in the qualifying session by providing him slipstream.

"If your results are poor you become a supporting team player, in the closing stages of the season – which of course doesn't offer you the opportunity to improve your own championship position."

Green said that 2018 taught him "what he shouldn't do" in pursuit of success.

"As a sportsman, such an experience helps you keeping your feet on the ground," he said. "That's important.

"I'm no arrogant person. If you celebrate major successes you mustn't get high-spirited.

"In the past 14 years I very often was among the front runners. For some people, such a drop in performance is shocking. I also was shocked.

"We didn't squeeze the maximum out of the car. I have to try to be more flexible regarding my style of driving, in the future, and respond faster if the car isn't in the window."

Green is yet to be confirmed for the 2019 DTM season with Audi, saying "we will have to wait for Audi's nomination".