Charles Barkley is going to bat for his old friend, Tiger Woods -- saying people like Jack Nicklaus who say Tiger needs help don't REALLY know what they're talking about.

Barkley appeared on 97.5 FM The Fanatic Philadelphia on Wednesday and was asked for his thoughts on Tiger's DUI. He's clearly upset with people assuming Tiger has a serious substance abuse issue. 

"Even Jack Nicklaus, somebody I really respect, talking about, 'Tiger really needs help.' Well he don't KNOW that. We don't know if Tiger has a drug problem."

Barkley added, "He just had a bad reaction [to prescription medication]. He wasn't out there drinking and driving."

Barkley says the "haters" are "in heaven right now because they get a chance to dump on the guy."

Barkley and Tiger were very close friends before 2009 -- and would regularly hit Vegas together. But Tiger cut him off after his marriage fell apart.