Wrestling icon Kevin Nash says pro athletes should be all about the green ... telling us tokin' up to treat pain is a much better option than pills.

Nash -- who was a badass in both the WWE and the WCW back in the '90s -- explained why he thinks herbal therapy is the way to go ... and he sounds like he's done his homework on the issue.

Check out the clip -- Nash also talks pot politics in his home state of Florida.