ST. LOUIS -- As expected, the D-backs placed Merrill Kelly on the injured list Tuesday with a right shoulder strain.

Kelly was scratched from Sunday's start at San Francisco and flew back to Phoenix for an MRI on Monday. The 35-year-old right-hander said he felt the shoulder grab while playing catch on Saturday.

D-backs Manager Torey Lovullo said there is no timetable for Kelly's return.

"He is definitely in a non-throw situation and just taking it day by day with treatment, trying to get him asymptomatic," Lovullo said. "And there's clearly going to be some re-imaging in the coming weeks to find out how he's healing and what we can do to push this forward."

Lovullo noted that the injury is a non-surgical situation.

The D-backs also placed right-hander Miguel Castro on the IL with right shoulder inflammation and recalled lefties Tommy Henry and Andrew Saalfrank from Triple-A Reno.

Kelly was off to a strong start to the season, with a 2-0 record and a 2.19 ERA. He has been one of the most consistent pitchers in baseball over the last four seasons and the one-two punch he formed with Zac Gallen at the top of the rotation helped fuel Arizona's run to the World Series last fall.

Lovullo said on Monday that right-hander Slade Cecconi will continue to take Kelly's spot in the rotation. Cecconi allowed just one run in six innings filling in for Kelly on short notice on Sunday.

Kelly told reporters on Sunday that the issue is with the teres major in his shoulder.

"That's the main focus," Lovullo said. "What level the concern is, is yet to be determined. So, that's what we're still trying to figure out. We're trying to take as deep a dive as possible. So, that is the area of focus. But the severity and the time down is still being defined right now."

The D-backs have been snakebitten by injuries this season.

Lefty starter Eduardo Rodriguez (lat strain) and closer Paul Sewald (oblique strain) were sidelined in Spring Training. Shortstop Geraldo Perdomo (right meniscus tear) and outfielder Alek Thomas (strained left hamstring) were hurt and placed on the IL after the season started.

And right before Kelly went down, right-hander Ryne Nelson was placed on the IL after getting hit by a line drive against the Giants on Thursday.

Lovullo called the rash of injuries "heartbreaking."

"I hurt for the athlete, hurt for the player, who just wants to be out there performing," Lovullo said. "And when that gets taken away from them, that's the worst thing a player could go through, the time down because of an injury. A lot of times, it's not their fault."

Lovullo said he goes through a process of self-evaluation to make sure over or under usage isn't a contributing factor.

"We tried to find the sweet spot here and I worked really hard at that," Lovullo said. "So, I have to check myself. I'm trying to do my own personal evaluation to see if I'm responsible for this. So, these aren't easy things."