CHICAGO >> Tony Gonsolin joined the Dodgers on Sunday morning in Chicago, and Dave Roberts acknowledged he was “here for a purpose.”

That purpose will be to start Wednesday in Pittsburgh, taking over the spot in the rotation left vacant when right-hander Michael Grove went on the injured list with a strained groin muscle suffered during his start Thursday against the Chicago Cubs.

Gonsolin made just one start in the Cactus League this spring before spraining his left ankle during a fielding drill. He opened the season on the injured list with a projected return in late April.

The right-hander threw to hitters at Camelback Ranch multiple times before joining Triple-A Oklahoma City on a rehab assignment this week. He pitched into the fourth inning for OKC on Thursday night, allowing one hit (a two-run home run) while striking out seven of the 12 batters he faced.

The expectation was for Gonsolin to make at least one more rehab start to continue building up his pitch count. But Grove’s injury changed that plan.

“He was going to come back anyway,” Roberts said. “He feels good about it. He’s on board with where he’s at as far as the buildup. He’s the best option right now.”

The other options were limited. Roberts said earlier that top prospect Gavin Stone would be “in the conversation.” But the Dodgers would prefer Stone continue refining his skills in Triple-A. He had his best start of the season so far Saturday, pitching 4 2/3 scoreless innings, striking out seven and allowing just two hits.

Smith’s status

Catcher Will Smith said he is “feeling better” and gradually increasing his activity level again. But for a few days, he was doing “not much.”

“Just have to let the brain heal,” he said. “There really is no way to know (how long it will take to recover from a concussion). Sometimes it’s two days. Sometimes it’s two weeks.”

It has been almost two weeks since Smith took multiple foul tips to the mask during a game in San Francisco. Two days later, he started experiencing concussion symptoms — mostly headaches, Smith said.

Impatient to get back in action, Smith said he probably tried to resume activities too quickly and the headaches returned, forcing him to “wait it out a few days.” He resumed activities Saturday and said he has been symptom-free over the past two days.

Smith is not expected to come off the IL until next weekend at the earliest now. He might go on a rehab assignment first to see if symptoms return with game action.

Who’s at short?

Mookie Betts made his first career start at shortstop Sunday. The move allowed Roberts to start three left-handed hitters in the outfield (Jason Heyward, James Outman and David Peralta) against Cubs right-hander Marcus Stroman.

Roberts wouldn’t say how often Betts might continue moving to shortstop, but did say it would be a consideration during the three-game series in Pittsburgh when the Pirates are expected to start three right-handed pitchers.

Injured shortstop Miguel Rojas has increased his workouts, taking batting practice on the field Sunday and taking ground balls at shortstop. Rojas is on the IL with a hamstring injury but could be ready to return when he is eligible to be activated next weekend.

“He’s doing much better,” Roberts said. “He already ran. He’s going to hit, take some ground balls today.

“He’s pretty encouraged about being ready when needed.”