OAKLAND -- The A’s will kick off their four-game series against the Rays without their head man in charge.

Manager Bob Melvin took a planned day off on Thursday for a doctor’s appointment after feeling discomfort in his back/neck area over the past couple of weeks. Ryan Christenson, the A's bench coach, will serve as the acting manager on Thursday night against the Rays, while quality control coach Mark Kotsay will fill in as bench coach.

“He’s doing fine,” Christenson said. “He’s going to the doctor to try to pinpoint where the pain is. They’re trying to alleviate that pain and get back to feeling well.”

The A’s said the issue is nothing serious and Melvin is expected to return to the club on Friday.

Managing a club is not foreign territory for Christenson. His impressive resume at the Minor League coaching level includes a Texas League Manager of the Year award in 2016 as manager of the Double-A Midland Rockhounds. Knowing he would manage on Thursday after discussions with Melvin over the past few days, Christenson said he has a pretty good idea of how to run a game similarly to Melvin.

“There are a little nerves there being here by myself, but I have [Kotsay] here who’s been with Bob for many years. We’ll be fine,” Christenson said. “I’ve been very observant over the last couple of years watching how Bob likes to run a game, so nothing really changes on the gameplan.”

Estrada throws on flat ground

Marco Estrada threw 15 pitches on flat ground, all fastballs, before Thursday’s game against Tampa Bay. The next step is to throw a bullpen session, which could come as early as Saturday. The right-hander has been on the injured list since April 17 with a lumbar strain.