Scott Weiland's Friends Panicked He Was Off Wagon with Crack

Some legendary musicians were in touch with each other 4 days before Scott Weiland died ... worrying he had fallen off the wagon again, and was deep into crack cocaine.

Our music sources say Scott had NOT slipped back into heroin abuse -- something that had plagued him during much of his adult life. But we're told crack, as well as heavy drinking, were front and center in the days before he died.

One source -- a huge rock star -- got a call before TMZ broke the story ... from someone connected to Scott who said he had died at around 7:30 PM of a drug overdose. Authorities in Minnesota have not confirmed this with TMZ.

One day before his death, Scott was on SiriusXM talking about his tour ... and challenging ISIS.