Michael Madsen was making enormous strides in his recovery from alcoholism … right up until just before his tragic death.

Sources with direct knowledge tell TMZ … Madsen was sober in recent months, making a consistent and valiant effort to turn his life around. But, those close to him remain uncertain about his state of mind in the days leading up to his passing. Everyone around him was hoping and believed he was still working his program.

The beloved actor spent years in and out of rehabilitation programs as he battled alcohol addiction … while also struggling with depression and grappling with personal hardships, like a troubled marriage — and his son’s untimely death. We are told he was constantly in and out of phases of trying to get his alcoholism under control.

As we reported … the “Kill Bill” star was found unresponsive in his Malibu home last Thursday and was pronounced dead at the scene. His rep told us he suffered cardiac arrest, while an official cause of death hasn’t been released.

It is unclear as of now if he had been drinking in the days leading up to his death … or whether alcohol played any factor at all.

Madsen’s longtime friend and assistant Dougie Smith revealed to us the actor appeared in good health nearly a week before his passing, after a routine doctor’s appointment for his rotator cuff … making his death all the more shocking.

Michael was 67.