'Bachelorette' contestant Tyler Gwozdz -- who competed for Hannah Brown -- was hospitalized for at least a week following a suspected overdose ... TMZ has learned.

According to Boca Raton PD, officers and paramedics rushed to a home on Monday, January 13 ... responding to a 911 call for a possible drug overdose. They ended up transporting Tyler to a hospital where he was admitted to the ICU.

We know Tyler remained in the hospital for a week and was listed in critical but stable condition. Come Tuesday, he was no longer a current patient in their system.

It's unclear what exactly led to the suspected OD, but according to the 911 call -- which we heard -- a woman told dispatchers it might've been heroin. The caller was frantically trying to get into a bathroom where Tyler had locked himself.

Eventually, she did break through and turned him on his back before an ambulance arrived.

Tyler was briefly featured during season 15, but was mysteriously sent home after 3 weeks on the show and a one-on-one date with Hannah. His removal was never explained -- all Hannah had to say was Tyler "had to leave."

Tyler's 'Bachelorette' profile says he was a sales manager when he was cast and he aspired to be a psychologist. The 29-year-old described himself as an entrepreneur who'd launched a dream therapy analysis biz.

We've made multiple attempts to contact Tyler and his family, but haven't heard back.