TMZ Sports broke the story ... the 21-year-old rookie visited the Herban Legends recreational weed dispensary -- which is fully LEGAL in the Seattle area.
Our sources say Elliott did NOT buy or smoke anything in the store -- but the fact he was there didn't sit well with his boss.
"Well, I think that in and of itself the reason we are talking about it is in a way part of the learning process," Jones said about the pics to the Star-Telegram after Thursday night's game.
"But it's not good. It's just not good. It's just not good."
Despite the visit, Elliott played pretty well during the game -- racking up 48 yards on 7 carries ... with some pretty bullish runs.
Still, Jones says, there's a lesson Elliott needs to learn.
"No matter if you played at whatever level there is a picture here of interest. So again, I’m aware of it. I heard the report and I would know how he is. And he needs to look at that and the other thing is it’s just not good. I don’t want to say anymore. I do want us do things that in general while it may not be wrong it’s just not good."