BOSTON -- Joe Kelly didn't feel like himself in the days leading up to his start Tuesday night at Fenway Park, and he was unable to get loose in the bullpen before the game. But he didn't say anything, believing he could push through the soreness that morphed into a pinching sensation whenever he tried to unleash a fastball against the Tampa Bay Rays.

Now the Red Sox right-hander might pay the price for his silence.

Kelly walked off the mound with athletic trainer Brad Pearson with two outs in the first inning of the Sox's 10-inning, 3-0 loss. He was diagnosed with what the team is calling a right shoulder impingement. He will be placed on the 15-day disabled list Wednesday but could miss considerably more time.

"It's really, really frustrating," Kelly said. "After I came out, I sat on my chair and ... it was something going through my head, pondering about what the next step is."

Kelly will undergo further testing Wednesday to determine the severity of the injury. Should Red Sox first baseman Travis Shaw be any guide, it was four-to-six weeks before he resumed throwing after being diagnosed with a shoulder impingement before the winter-ball season in November.

"I don't know the extent of Joe's injury or what happened," Shaw said. "I know mine, personally, ended up being more of a bigger deal. But we'll see how this one is."

In the minutes after Wednesday night's game, the Red Sox had not yet decided how they will fill Kelly's spot in the rotation. Left-hander Eduardo Rodriguez is at least two weeks away from being ready to rejoin the rotation after opening the season on the disabled list with a right knee injury.

Kelly ranked seventh in the majors in average fastball velocity (95.4 mph) last season, but he was clocked at only 89-90 mph to the first three batters of the game. He exhibited little command, threw only seven of his first 20 pitches for strikes and walked Logan Forsythe and Evan Longoria.

After Kelly fell behind 3-0 to cleanup hitter Corey Dickerson, pitching coach Carl Willis went to the mound but returned to the dugout without any indication from Kelly that there was a problem.

Joe Kelly walked two of the three batters he faced Tuesday before being removed from the game against the Tampa Bay Rays with a shoulder injury. Bob DeChiara/USA TODAY Sports

"Didn't complain of anything," manager John Farrell said. "There was maybe more changeups thrown in that first inning than we typically would see. When he's been most effective, we know that there's been a constant mix of pitches. He's gradually worked into his velocity. I thought that's what was taking place."

The next three pitches were all fastballs -- 92, 93 and a 94 mph heater that Kelly said was "all I got right there." He struck Dickerson out, but after his final pitch, catcher Ryan Hanigan and the infielders gathered at the mound. First baseman Hanley Ramirez motioned to the dugout, and after a lengthy conference with Farrell and Pearson, Kelly was replaced by reliever Heath Hembree, who had been called up from Triple-A Pawtucket earlier in the day.

"It was typical soreness leading up to the start," Kelly said. "Like I said, I thought I was going to be good to go and went out there and tried to step on the gas, and nothing came out. I was trying to push through the whole time, even when the medical staff and John came out. I was trying to push through it, and ultimately, they made a decision to take me out of the ballgame."

Kelly missed the final month of last season with a strained shoulder, an injury that both he and Farrell said is unrelated to this one. Kelly showed no hint of shoulder problems during a strong spring training. In his first two starts of the season, he gave up seven runs in three innings April 8 against the Toronto Blue Jays and two runs in five innings April 13 against the Baltimore Orioles.

"I had a good spring training and felt good last year," Kelly said. "The first start wasn't what I wanted, but [I] started to feel like I was going in the right direction. And then to have something like this is very disappointing."

Left-hander Henry Owens would be the likely choice to take Kelly's place. Owens has allowed only two runs in 18 innings over his first three starts in Triple-A, but he has walked 10 batters. The Red Sox could consider lefty Roenis Elias, who has a 3.86 ERA in two starts for Pawtucket but also has had trouble with command (seven walks in 9 1/3 innings).