Costa, 29, was tipped to become the next superstar of Brazilian football when he burst onto the scene with Gremio back in 2008 but after a long sequence of hamstring, calf and knee problems - he's failed to live up to his early potential.
Despite not reaching the heights expected of him, the fleet-footed winger still finds himself representing one of the biggest club's in world football but he concedes he's thought of calling it a day out of sheer frustration.
"There are times when I think: 'Can I still play?'" he told The Players' Tribune."[That's] because I go out on the pitch and get injured again.
"Then, when I watch it on TV, I remember this is my passion and that I can still play at a high level. This is what keeps me alive, I know football comes easy to me. It has nothing to do with money or being famous.
"The point is to do what you enjoy and have fun doing it. That's my objective. I joke with Alex Sandro that I've had more scans than I've played games."
The 31-time capped Brazil winger reached 30 league appearances only once in his career, which came during his loan spell in Turin in the 2017/18 season from Bayern Munich.
He also revealed that he's hired a mental coach to help deal with the psychological effects of the injury-ravaged seasons that's kept him from developing further.
"People say, 'Douglas has the potential to be one of the best in the world, but injuries are holding him back'. That annoys me," he said. "I have the potential to be a top player, but for reasons out of my control I can't be.
"Every time I get injured, I ask myself: 'What did I do wrong?' I wonder why I can't play consistently. It's something that hurts me.
"Therefore, I asked for help. I don't know if you've heard of a mental coach. They're not a psychologist, but they show you how childhood facts can still affect you."