LOS ANGELES — Tyler Glasnow will join the Dodgers on their road trip to Arizona and will resume his pitching schedule Friday at Chase Field in Phoenix as he recovers from tendonitis in his elbow.

Glasnow last pitched for the Dodgers on Aug. 12, and Wednesday was his first day back from the injured list. But pain while pitching has turned his rehabilitation into a slow process, as his elbow hasn’t felt better as originally hoped.

Given the missed playing time, Glasnow will need to complete a minor league rehab assignment before he can return. With just four weeks left in the regular season, it will be a race against the calendar to potentially be ready for the playoffs.

It’s a similar position to that held by rotation mate Yoshinobu Yamamoto, who began a rehab assignment Wednesday night with two innings for Triple-A Oklahoma City.

But Glasnow must pitch first, and eventually battle batters. That first step comes Friday in Phoenix.

“If all goes well, we’ll see where he is at,” manager Dave Roberts said on Wednesday.

Brusdar Graterol threw a bullpen session at Dodger Stadium on Wednesday and will likely leave soon for a rehab assignment.

“The bullpens are good, the velocity is good, I don’t see why we can’t get him out there quickly,” Roberts said.

Graterol missed more than four months with shoulder inflammation, and in his first game back for the Dodgers on August 6, he strained his right hamstring and had to be airlifted off the field. At the time, it was thought Graterol’s season might be over, but the diagnosis improved to the point that he has recently returned to pitching, leading into Wednesday’s bullpen session.

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

Austin Barnes was given a simulated turn at bat against a minor league player for the second straight day Wednesday at Dodger Stadium and is expected to come off the injured list Thursday, his first day back.

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