Ray J is laid up in a hospital bed after getting knocked out in his celebrity MMA fight ... and TMZ has photos of him with all sorts of monitors hooked up to his body.

In the images, obtained through a rep for Ray J, you see him shirtless and under some covers in a hospital bed ... in a couple snaps, he's looking up towards the ceiling and in another he's got his eyes closed as he sleeps and tucks his arms under a pillow.

Sources close to Ray J tell TMZ ... Tuesday marks Ray's third day in a Las Vegas hospital, and he's going to remain hospitalized for a few more days.

Depending on how long he's in the hospital, Ray may miss his son's graduation. He's already missed Memorial Day weekend with his family after fighting Supa Hot Fire on Saturday and getting knocked out.

As we reported ... Ray checked himself into a hospital a couple hours after the KO ... with doctors running a battery of tests to figure out if he had a concussion and/or heart issues.

It's Ray's second hospital stay this year ... he battled pneumonia before the fight.