The Houston Police Department says it's now launched a criminal investigation into Deshaun Watson ... this after a complainant formally filed a report against the NFL star on Friday.
Cops did NOT say the nature of the allegations against the QB ... and it's unclear if they're related to the claims of sexual assault that Watson is facing in a multitude of civil lawsuits.
In a statement Friday, though, Watson's attorney implied they may be.
"We welcome this long overdue development," Rusty Hardin said.