Robert and his son, Jonathan (who's the president of the Patriots) spoke about the troubled WR on "Boston Sports Tonight" ... calling Gordon a "real good guy" with incredible potential.

The Patriots signed Gordon in Sept. knowing full well his history with substance abuse -- but figured they could give him a support system to overcome his demons.

27-year-old Gordon crushed it for the Pats until Dec. -- when he was suspended by the league after reportedly falling off the wagon, and failing another drug test.

"Unfortunately, people like that need mentoring at a young age," Robert said.

"But, when it becomes addiction, addiction is something that is way beyond our ... we gave him tremendous support on a daily basis, and he was worthy. But, I think we as a society have to try to help these young people not to get addicted in the first place."

"And, that's the sad part of this. He's a good guy -- a really good guy. It makes us sad."

Jonathan echoed his father's sentiments ... saying Gordon clicked with his teammates, had a great work ethic and could have been a key contributor in the playoffs -- if he could have stayed clean.

"This wasn't a troublemaker in the locker room," Jonathan said ... "Unfortunately, he had some personal demons."

"As a person and as a teammate, he was beloved in the locker room. And, I'm sure if you ask guys this week, they would tell you they wish he was here with us. He was not a guy that was disruptive or a problem."

Both Jonathan and Robert believe Gordon's issues run very deep -- and his story is a wake-up call about how to prevent addiction in the first place.

"He didn't grow up with any support system," Jonathan added ... "He saw other people doing it, and it gets back to the original way we grew up."

"And, that doesn't mean people don't get addicted from all walks of life -- but you get exposed to it in a whole different way when you come from where Josh Gordon came from. He is a very good kid."