Dodgers head athletic trainer Sue Falsone had a busy day Thursday — a day off for the team, but hardly a day off for the trainer with a disabled list of eight players.

Justin Sellers became the latest addition as he took the place of Jerry Hairston Jr. on Friday. Hairston was in the starting lineup and Sellers was reduced to performing core exercises after an MRI Thursday revealed a slipped disc as well as a stress fracture in his lower back.

The injury is related to the head-over-heels catch Sellers made May 14 –but not entirely.

“He had what’s called a spondylolysis, or a stress fracture, back in high school,” Falsone said. “A lot of younger athletes have it. A lot of older athletes have it. It’s no big deal — a little stress fracture in the back.”

Falsone went on to explain that the stress fracture created an area of weakness that was exacerbated when Sellers tumbled into the stands. At first he reported back pain, then numbness down his right leg from the hip to the toe.

Both Sellers and Falsone were optimistic that he would only need the minimum 15 days on the disabled list, but “if it doesn’t get better, we might have to remove part of the disc,” Sellers said.

The infielder is hitting .205 with three doubles and a home run in a reserve role.

Hairston’s name was penciled into the starting lineup (batting fifth, playing third base) for the first time since May 6, when he first strained his hamstring in Chicago.

“I was playing quite a bit (at the time of the injury). I don’t know if (my role) will change or not,” Hairston said. “I was on three or four, then maybe an off day, so on and so forth. I’m always ready to play no matter what.”

In two rehab games with the Triple-A Albuquerque Isotopes, Hairston went 0-for-6 while playing left field, second base and third base.

Mark Ellis wasn’t at Dodger Stadium Friday, but manager Don Mattingly said he expects to see the second baseman soon after Ellis was released from a local hospital Thursday.

Ellis has a sprained medial collateral ligament as well as a contusion on the outside of his left knee, Falsone said, “which makes complete sense if you really watch that play, as far as what he did and what happened.”

Here’s another look at that play, with a good breakdown around the 36-second mark:

Falsone said that she expects it will take eight weeks “for everything to heal.” That projects to July 20, about a week after the All-Star break, but there’s no guarantee that Ellis would be able to play immediately.

Third baseman Juan Uribe is in Glendale, Arizona, where he took ground balls and did “light stuff with a bat,” Dodger manager Don Mattingly said.

Juan Rivera and Matt Kemp, both recovering from strained hamstrings, ran close to full speed before the game. Both are on track to begin rehab assignments at Albuquerque this weekend.