LOS ANGELES — Tyler Glasnow will join the Dodgers on their road trip to Arizona, and resume his throwing program on Friday at Chase Field in Phoenix, as he works his way back from elbow tendinitis.

Glasnow last pitched for the Dodgers on August 12, and Wednesday was his first day eligible to return from the injured list. But feeling soreness while throwing has turned his rehab into a slow process, as his elbow hasn’t felt better like what was originally hoped.

Given the time missed, Glasnow will need a minor league rehab assignment before returning, and with just over four weeks remaining in the regular season it becomes a race against the calendar to be potentially ready for the postseason.

It’s a similar position as rotation mate Yoshinobu Yamamoto, who started a rehab assignment with two innings Wednesday night for Triple-A Oklahoma City.

But up first for Glasnow is throwing, and then eventually facing hitters. That first step comes Friday in Phoenix.

“At that point in time, if all goes well, we’ll see where he’s at,” manager Dave Roberts said Wednesday.

Brusdar Graterol threw a bullpen session on Wednesday at Dodger Stadium, and will likely head out on a rehab assignment shortly.

“The bullpens are good, the velocity is good, I don’t see why can’t send him out soon,” Roberts said.

Graterol missed over four months with shoulder inflammation, then in his first game back for the Dodgers on August 6 strained his right hamstring, and had to be helped off the field. The thought at the time was that Graterol’s season might be over, but the diagnosis improved to the point that he’s been throwing recently, leading to Wednesday’s bullpen session.

“Considering where he was after his first outing back with us, and to have this conversation about early September, it’s great,” Roberts said. “Brusdar has just been so valuable for us each year, and in the postseason.”

Austin Barnes got simulated at-bats against minor league for a second day in a row at Dodger Stadium on Wednesday, and is expected to be activated off the injured list on Thursday, his first day eligible to return.

Barnes was placed on the injured list on August 19 with a fracture in his left big toe. Roberts said Barnes would start in the series finale against the Orioles.