WALTHAM — Doc Rivers paraphrased Bill Parcells following Thursday’s practice that didn’t include injured forwards Semih Erden and Jermaine O’Neal.

“This is who we are right now,” Rivers said in announcing the latest injuries to hit the Celtics’ front court.

Jermaine O’Neal had an MRI Thursday on his sore left knee that acted up in the second half of Monday’s game against Houston.

Rivers is concerned that surgery will likely be needed to correct the issue.

“Don’t know yet,” Rivers said following practice Thursday. “I know he did [have] an MRI. Honestly, my guess is they’re going to have to do something. So, I don’t know that. I’m just using my doctorate right now. My guess is they’ll probably have to do something.”

Complicating matters is a groin pull sustained by back-up center Semih Erden, which kept him out of practice Thursday and limited the Celtics to nine healthy players. With Kevin Garnett still out with a strained right calf, Kendrick Perkins (right knee) not yet cleared for contact practice and Shaquille O’Neal getting limited minutes to save his stamina for later in the season, the Celtics are struggling with depth in the front court.

“It puts more pressure on them,” Rivers said of his remaining healthy front-court players. “Semih couldn’t practice today. He has a groin pull. So, that’s what we are. We have 15 players. We’re going to send Avery [Bradley] down [to D-League] pretty soon, too, so he can get some reps playing basketball. I just think he needs to play basketball. It’s part of it.”

The Celtics face Charlotte on Friday night at TD Garden as they continue their season-long six-game homestand, likely without Garnett, Erden and Jermaine O’Neal.