Ex-49ers RB Jarryd Hayne

Former 49ers RB Jarryd Hayne -- who was also a massive international rugby star -- was convicted of sexual assault Monday ... and he's now facing serious time behind bars.

A jury in Sydney, Australia found the 33-year-old guilty of two counts of sexual intercourse without consent ... this after a woman had accused Hayne of getting violent with her in bed in Sept. 2018.

The woman claimed Hayne had performed sexual acts on her without her consent ... and caused her serious injuries.

Hayne -- who was ultimately charged with aggravated sexual intercourse without consent as well as two counts of sexual intercourse without consent -- had denied the allegations, insisting it all was consensual and…