The NFL has confirmed they're launching an investigation into Jalen Hurts' medical care and blood clot diagnosis ... after the player was sidelined for the rest of the season.

The league confirmed the probe into about how the Philadelphia Eagles handled the diagnosis in a joint statement with the National Football League Players Association Sunday.

Their statement reads ... "The NFL and NFL Players Association are working together to review the matter."

The investigation comes after the NFLPA demanded a full inquiry be made by the league into how his medical treatment was handled.

They wrote last week ... "Before conclusions are drawn about how this situation was handled, there must be a full investigation into what occurred. Determining the facts is essential to ensuring players receive the highest level of care and protection going forward."

As you know ... Hurts was initially diagnosed with a superficial blood clot in his leg ... before the clot spread to his lungs where multiple clots were found.

Hurts is now out for the remainder of the season ... and based on what we're hearing, it's imperative he stay off the field.

Doctor David Abbasi told Jakson on TMZ's "In The Know" ... the star athlete could be out for 3 to 6 months due to the risk of incurring serious damage from bleeding.