ST. PETERSBURG -- The Rays announced Saturday that Tyler Glasnow's MRI on Friday night revealed a mild right forearm strain, and he is expected to miss four to six weeks.

Glasnow, who exited Friday's game in the sixth inning with forearm tightness, has been placed on the 10-day injured list, and he will be shut down from throwing for seven to 10 days before being re-evaluated.

Losing Glasnow is another injury blow for the Rays, who already have Mike Zunino, Michael Perez, Matt Duffy and Joey Wendle on the injured list. But all in all, the timetable for a return could be seen as positive news as injuries to the throwing arm could result in something even more severe.

"I was excited," Glasnow said of his reaction after learning it wasn't a season-ending injury. "I mean, three to six weeks is better than 16 months or whatever it is, so I was optimistic, for sure."

"You never fully know until he's ramped back up and gets going," Rays manager Kevin Cash added. "But we're optimistic by the early results that it's not anything that's going to prevent him from missing a substantial amount of time."

Glasnow, who won American League Pitcher of the Month honors in April after posting a 6-0 record, has been one of the best pitchers in the Majors this season and his 1.86 ERA leads the AL, even after allowing a season-high three earned runs on Friday against the Yankees.

The right-hander said he's obviously upset that he'll have to miss time, but added that he would look at the injury as a positive and come back to help the Rays make a push for the playoffs over the last couple of months of the season.

"You can look at it as a negative or a positive and I'll choose to look at it as a positive," Glasnow said. "I'll come back mentally and physically stronger, but I think there's a mental aspect to it, to going through something like this, that makes you a lot stronger mentally. I'm honestly just looking forward to pulling all the positives that I can out of the experience."

With Glasnow out for at least the next month, the Rays will rely on starters Blake Snell and Charlie Morton and bulk guys Yonny Chirinos and Jalen Beeks to help fill the void left by the 6-foot-8 right-hander.

The injury leaves the Rays with just two starters, and Cash said the team is still unsure of what the plan is going to be with the rotation. The Rays, however, could opt to stay flexible with their pitching plans and have multiple arms try to fill the spot in the rotation, with Chirinos, Beeks, Ryan Yarbrough and Jake Faria as possible options.

"We've got some time with the off-days, so we don't have to rush into a decision," Cash said. "Obviously the candidates are Yonny, Jalen, Yarbs and we'll see how we continue to build them up. They're all pretty stretched out now, and [we'll] just see when those days fall when we have to have that fifth starter or fifth option come available in the next go-round.

"But we do have some time. It's a good thing because if we didn't have the off-days, we probably would have to make those decisions right now, but we don't."

With Glasnow going on the injured list, the Rays called up infielder Andrew Velazquez to take his place on the active roster. The Rays also activated catcher Travis d'Arnaud, whom they acquired from the Dodgers for cash considerations on Friday, and optioned Nick Ciuffo to Triple-A Durham.

"Ciuffo needs to go play," Cash said. "That was kind of the message to him. He's still a young, and he needs to get consistent reps. If he's not going to get consistent reps up here, it makes the most sense for him to do down [to Durham]."