A 25-year-old Miami man could be facing kidnapping charges after cops say he held a 19-year-old homeless woman against her will for several days.

Detectives say the two met online, and she called 911 after he didn't let her leave his house.

The guy's sister claims the woman is making the whole thing up...

But cops say 911 operators heard an assault over the phone and the man telling the victim she couldn't leave.