It's been nearly a year since Serena Williams gave birth to her first child and, although she has returned to playing competitive tennis this year, her battles are not just limited to the court anymore. 

In an Instagram post shared on Monday, the 36-year-old Williams opened up about her recent struggles with postpartum emotions and how they've left her in a "funk" over the past week or so.

Last week was not easy for me. Not only was I accepting some tough personal stuff, but I just was in a funk. Mostly, I felt like I was not a good mom.

I read several articles that said postpartum emotions can last up to 3 years if not dealt with. I like communication best. Talking things through with my mom, my sisters, my friends let me know that my feelings are totally normal.

It's totally normal to feel like I'm not doing enough for my baby.

We have all been there. I work a lot, I train, and I'm trying to be the best athlete I can be.

However, that means although I have been with her every day of her life, I'm not around as much as I would like to be. Most of you moms deal with the same thing. Whether stay-at-home or working, finding that balance with kids is a true art. You are the true heroes.

I'm here to say: if you are having a rough day or week--it's ok--I am, too!!! There's always tomm!

Williams made an impressive run to the Wimbledon finals (where she ultimately lost to Angelique Kerber) earlier this summer, but she hasn't seemed like her dominant self of late. She withdrew from the Rogers Cup, then was defeated in the first round of last week's Mubadala Silicon Valley Classic. That loss to Johanna Konta was the most lopsided match of Williams' professional career.

And while those professional struggles grab the majority of headlines, Williams has decided to open up and be honest about the struggles she's dealing with personally behind the scenes. Her heartfelt message shared Monday is an important one, and one that many parents can undoubtedly relate to. 

To many, it might not seem like much. But those who struggle with mental health issues or rough patches in various areas of their personal life -- whether it be parenthood, family life, romantic relationships or just friendships -- it's valuable to know that other people are going through it too. 

Sending the message that it's OK to not be OK can make a big difference, especially when it comes from someone who is as well-respected and accomplished as Williams.