The image found Anna standing in a carpeted room a long sleeve black shirt with the sleeves rolled up and over-the-knee socks.
Opting for the shock factor, the blonde beauty sported just a tiny pair of nude hot pants - which appeared to look like Spanx control underwear.
She captioned the photo: 'Having pre-show jitters- so glad Michael Sherman captured it- also I eventually decided to put on pants.'
The post was met with a flurry of negative responses with unkind fans lashing out at the star's svelte frame - going as far as a user branding the shot 'alarming'.
Despite the unkind comments, TMZ unearthed a comment from one supporter with the fan writing: 'You are beautiful at any size. Health is our concern. If you're healthy and happy that's all that matters! Continue to be awesome!'
In the past, Anna has spoken candidly about her figure, as in 2013 she revealed her busy work as an actress helps keep her svelte.
The blonde beauty said: 'This job, unlike other jobs I've been on, keeps me on my feet all day long. I'm never in my dressing room. So I'm like running all over. Also, my dressing room's upstairs."
It's been a rough 13 months for Anna, who split from her husband of nine years, Chris Pratt, in August of 2017.
She has been able to find new love with cinematographer Michael Barrett, who she has been dating since last November. She shares five-year-old son, Jack, with Pratt.
Where to get help:
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111.
Or if you need to talk to someone else:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Need to talk? Free call or text 1737 (available 24/7)
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• Samaritans 0800 726 666
• Rural Support Trust: 0800 787 254.