The Belgian former world number one wants to take it as a challenge and not to prove anything.
"I don't really feel like I want to prove something. I think for me it's the challenge," Clijsters was quoted as saying by the BBC.
Speaking to the WTA Insider Podcast, she added: "The love for the sport is obviously still there. But the question still is, am I capable of bringing it to a level where I would like it to be at and where I want it to be at before I want to play at a high level of one of the best women's sports in the world?
"I want to challenge myself and I want to be strong again. This is my marathon."
Clijsters first called it a day in 2007 to start a family but returned two years later and won two more US Open titles and the Australian Open before her second retirement in 2012.
Clijsters can get unlimited wildcards at WTA tournaments as she was a world number one. She will require to feature in three tournaments or earn 10 ranking points to re-establish a ranking.