Evans, 39, shared a screen recording of himself playing Heads Up with his family, but at the end of the clip people caught a quick glimpse of a camera roll - with one picture being of a man's genitals, along with another of Evans' face with text that said 'Guard that p***y'.
Evans is yet to address the post, which was deleted shortly after, and there has been no confirmation about whose camera roll was displayed.
However, Ruffalo has stepped in and said something, pointing out that things could be a lot worse.
Tagging his pal on Twitter, Ruffalo wrote: "Bro, while Trump is in office there is NOTHING you could possibly do to embarrass yourself. See... silver lining."
While many people managed to take screenshots of the explicit image and shared them on social media, others have called on fans to respect the actor's privacy.
One tweeted: "Everyone has seen a penis before. There's no need to see this particular person's penis. Leave Chris Evans alone."
Another wrote: "Before sharing Chris Evans nude, remember that the actor suffered an anxiety disorder with the rise of his Hollywood career and even refused to be Captain America on several occasions for fear that fame would affect him and his family."
Some even shared alternative photos of the star to help fill feeds with more 'wholesome' images, promoting a feeling of positivity and support.
Back in May, Evans revealed he felt joining that Marvel Cinematic Universe was the 'best decision' he'd ever made, but said it almost didn't happen as he'd been suffering panic attacks while working on the film Puncture in 2010, and worried his anxiety might hold him back.
Speaking to The Hollywood Reporter on its Awards Chatter podcast, Evans said: "It was the first time I started having mini panic attacks on set.
"I really started to think, 'I'm not sure if this [acting] is the right thing for me, I'm not sure if I'm feeling as healthy as I should be feeling.'"
He continued: "It was the best decision I've ever made, and I really owe that to [Marvel Studios president] Kevin Feige for being persistent and helping me avoid making a giant mistake.
"To be honest, all the things that I was fearing never really came to fruition."
Featured Image Credit: Marvel