Shaquille O'Neal On The Mend After Undergoing Hip Surgery

Shaquille O'Neal sparked concern after sharing a photo of himself in a hospital bed on Sunday ... but TMZ Sports has learned the NBA legend simply needed to fix a nagging injury, and he's now doing OK.

Our sources tell us the 51-year-old went under the knife over the weekend to have an issue with his hip corrected -- and everything went according to plan. We're told he's already on the mend.

In a caption Shaq posted along with the photo -- he tagged his "NBA on TNT" colleagues, Ernie Johnson and Candace Parker, saying even though he couldn't be at work, he was still tuning in to the show.

"Miss y’all," he wrote.

Parker, a two-time WNBA champ, responded, "Love ya big Fella ♥."

It's unclear when Shaq will return to his TV gig -- our sources say there's no set time frame -- but in discussing the upcoming procedure earlier this month on his podcast, "The Big Podcast With Shaq," he seemed to say he had April 16 in mind for when he could be active again.

He added on the pod that he was going to go on a diet to get "shredded" after the surgery ... and eventually reveal an 8-pack!!