NBA's Larry Nance Jr. Reportedly Lost Nearly 20 Lbs. In 1 Week Due To Mystery Illness

Scary situation for Larry Nance, Jr. -- the Cleveland Cavaliers forward reportedly lost nearly 20 POUNDS in just over a week while battling a non-COVID-related illness.

But, luckily, the 28-year-old is starting to show signs of improvement and is "on the mend."

Nance came down with the mystery illness on March 29 while in Utah for a road game ... and hasn't played a minute of basketball since.

The details are now coming out about the hooper's symptoms -- and it's gnarly.

Nance spent the past week and change bedridden and unable to keep food down, according to cleveland.com ... all while getting consistently tested to help determine what he's fighting.

It's NOT COVID-19 ... but it's still unclear what exactly he's dealing with.

The report says Nance has experienced a DRASTIC weight loss in the short amount of time ... losing 20 pounds in a little over a week.

The good news?? Nance is starting to feel better ... and will slowly work on getting back to his reported weight of 245 lbs. and rebuild his stamina.

It's been a tough year for the guy -- Nance also previously missed 12 games while battling a fractured left hand.