The Prophet Muhammad (peace & blessings upon him) was not concerned with his followers falling for literal idolatry.

The Oneness of Allah just makes far too much sense and it's unthinkable that anyone who believes in the Quran would literally start intentionally worshipping something else.

However, subtle forms of idolatry, like showing off (i.e. valuing what other people think more than Allah) and other diseases of the heart can be devastating to the soul.

Perhaps one of the most subtle forms is what I call, "Psychological Idolatry".