Marino revealed Wednesday she's receiving treatment for depression, but said her primary reason for stepping away from tennis again is she no longer wants to live the isolated, nomadic life of a pro.
The 22-year-old from Vancouver reached a world ranking of 38th two years ago. Marino did not say she's retiring, but has no immediate plans to return to the game.
"I have previously been to number 38 on the WTA singles rankings so I realize the amount of work and sacrifices that have to be put in," Marino told reporters during a conference call.
"At this point, I don't feel it is worth sacrificing my happiness for."
Marino went from No. 192 in the world to 2010 to No. 38 a year later.
She waged a memorable battle with Venus Williams before bowing out in the second round of the 2010 U.S. Open. Marino reached the final of a WTA tournament in Memphis the following season.
But the Canadian abruptly dropped out of tennis for seven months a year ago. She returned to competition in the fall and won a WTA Challenger event in October.
She lost in the first round of the Australian Open in January. Her world ranking has dropped to 418th.
Marino explained Wednesday that she's suffered depression for several years, but it wasn't until her break from the game a year ago that she sought treatment.
"I've had days where I haven't been able to get out of bed," she said.
"I have days where I can't even put my clothes on. It's hard to describe where you have this smothered feeling of grey and lack of motivation to do things.
"I'm doing much better, but I still have those days where I can't find the motivation to get up. That's why I have my friends and family and I have a therapist who supports me and they get me through everything."
Marino started travelling to play tennis at 13. She took her Grade 12 by correspondence.
At the age of 17, Marino spent half a year in Switzerland and at 19, she moved from Vancouver to Montreal to train at the National Tennis Centre.
Living away from her support system was difficult for a young woman dealing with then-undiagnosed depression.
Marino had told the New York Times that she found the criticism of her in social media overwhelming at times, but insisted that was not the reason she took herself out of the game again.
"My depression had come way before the cyberbullying," she said Wednesday. "This has been going for, I would dare to say, six years, my depression.
"Social media has also taken its toll on me. It's not the main reason I'm stepping back. Neither is the depression. The reason I'm stepping back is because I don't think I'm willing to sacrifice my happiness and other parts of my life to tennis."
Marino did say she intended to ignore social media for now.
"The hurtful ones kind of stick with you a little bit more," she admitted. "I was getting some messages saying I should go die, that I should go burn in hell, that I'm a dumb-ass, that I'm an idiot, that I lost them money.
"I just stepped away from social media last night or the day before just to get away from that because I knew with this press conference, a lot more comments would be coming through."
Marino says Tennis Canada was sympathetic and supportive when national team coach Sylvain Bruneau was informed a year ago of her depression.
"We tried everything we could in our power to help her achieve her dreams and objectives with her tennis," Bruneau told The Canadian Press prior to Marino's comments to the media.
"We've been very supportive all the way, from the very beginning when she's mentioned things. We're still very supportive of her decision because it's obviously what's best for her."
Marino considered not discussing her depression publicly, but wanted to assist others who might be dealing with the illness.
"I'd like to get rid of the stigma attached to depression and mental illnesses in the public and in professional sports," she explained.
"Depression is nothing to be ashamed of. If I can open up about my struggle to the public, I hope I can give someone the courage to seek the help they deserve."