Darren Sharper Rape Case -- TWO FEMALE VICTIMS ... Cops Say

TMZ Sports has learned ... former NFL superstar Darren Sharper is being investigated for allegedly raping TWO different women on two different nights.

We broke the story ... Sharper -- a 5-time Pro Bowler and Super Bowl champ -- was arrested on Friday in Los Angeles after cops say he's been linked to two sexual assaults.

Now, we've learned ... the case involves TWO accusers -- each of whom claim Sharper raped them in L.A. hotel rooms .. one in October 2013 and the other in January 2014.