Quinton Aaron -- the actor who played Michael Oher in "The Blind Side" -- has been hospitalized, TMZ Sports has learned, after he woke up last week with a bad illness.

The 40-year-old tells us ... he was rushed to a Southern California medical facility on Feb. 27 -- after coming down with a fever and a blood-soaked cough.

Aaron says doctors administered a bunch of tests ... and the early indications are he's dealing with Type A flu as well as pneumonia.

To make matters worse, Aaron tells us the whole ordeal has left him with a days-long migraine.

Thankfully, Aaron said on Tuesday after a round of antibiotics, he's no longer hacking up blood ... and he's hopeful that after doctors administer a PICC line, he'll be able to go home soon.

"I feel optimistic I’ll be back on my feet in no time," he said.

Aaron had been in Laguna Hills to perform and present at an event in Orange County ... though he told us his ailment forced him to ultimately miss the planned appearance.

Unfortunately, this is not the first time Aaron's had to go to the hospital with lung issues ... back in 2019, he spoke with us from a doctor's office while he was battling a brutal upper respiratory infection.

Get better soon, QA!