Eric & Charlie have been friends for years ... developing a relationship while Davis was a member of Sheen's beloved Cincinnati Reds.
TMZ Sports spoke to Eric ... and he told us regardless of what Sheen's critics might say about his lifestyle or choices ... he's in his corner while Charlie battles the virus.
"When you're someone's friend, it doesn't matter what trials and tribulations they're going through. When you're a true friend, your friendship doesn't waver."
Davis went on to say this isn't the first time he's had a famous friend go through an HIV diagnosis ... and he's ready to take the lessons he learned from that situation to help Charlie get through this.
"It's not the end of the world. I had another good friend who was diagnosed ... Magic Johnson. I saw how he managed and controlled it."
BTW Eric called in to the "TMZ Sports" TV show (Tuesday at 9pm PT on FS1) ... and told us what he plans to say to Charlie when he finally gets a chance to see him face to face.