"Any time a pitcher feels something in there, you have to take him out," said Gibbons, who opted not to speculate on the extent of Burnett's injury. "We don't think it's much, but I can't comment any more than that. We'll know more tomorrow."
Prior to Wednesday afternoon's series finale with the Giants, Burnett (5-6) will undergo additional testing to determine just how badly he's hurt. After leaving the game following his 82nd pitch, Burnett passed the initial tests performed by Toronto's medical staff, and he may be able to avoid a trip to the disabled list.
The 30-year-old pitcher is hoping that means he's simply fighting a bad case of fatigue, caused by a heavy workload in his recent string of starts. In Burnett's three previous trips to the mound, he threw 372 pitches, including a season-high 130 on Thursday for the Blue Jays (30-34).
"I've thrown a lot here recently," said Burnett, who allowed three runs in 4 2/3 innings. "So maybe I'm a little tired. I may need another day off -- miss a start or something. We don't know. All the tests were negative, so we're just going to get it checked out to make sure. I'm not too worried about it."
Burnett's teammates, on the other hand, were very concerned when the pitcher's shoulder flared up against San Francisco (30-34). Burnett has had eight stints on the DL over nine big-league seasons. Most recently, he missed more than two months last season due to a right elbow injury, which is unrelated to the current problem.
Given his history, and the series of injuries that have stricken the Jays this season, it was no surprise that some of the Jays immediately feared the worst. Already this year, Toronto has had 11 players land on the DL, including eight who are currently sidelined.
"Why wouldn't it happen to another guy?" said Toronto second baseman Aaron Hill, shaking his head at his team's misfortune. "Hopefully, everything's going to be fine. Maybe he'll just need some rest. Maybe he's a little fatigued. That's what we're praying for. We don't need another guy going down."
Gibbons said that the Blue Jays will be bringing another pitcher up in order to give an additional arm to the bullpen -- a group that recently lost Josh Towers when the Jays moved him back into the rotation. Toronto's manager would not say who the pitcher might be, but added that the club would try to have someone in San Francisco on Wednesday.
Losing Burnett overshadowed another dismal showing by Toronto's offense. Since churning out 11 runs on 16 hits in a win over the Dodgers on Sunday, the Jays have hit .210 with only five runs in two losses to the Giants. The one-run loss marked an American League-high 25th one-run contest of the year for Toronto.
On Tuesday, the only spark came from Alex Rios, who belted a 1-1 pitch from left-hander Noah Lowry in the third inning for a two-run home run -- the right fielder's team-leading 15th blast of the season. Lowry (6-5) picked up the win after turning in six strong innings for the Giants.
Hill had a potential game-tying homer robbed by Giants left fielder Randy Winn in the ninth inning. With one out, Toronto's second baseman sent a pitch to the wall, where Winn leaped and snared the ball.
"We're not scoring runs," Gibbons said. "We've been in every game -- it was another one-run game. We had the laugher on Sunday, but we've been battling. We've just been coming up one run short."
His injury issue aside, Burnett said he was disappointed he couldn't protect the early lead that Rios provided. With Toronto ahead, 2-1, the right-hander allowed a pair of runs on the third -- highlighted by a RBI single by Klesko. It was Klesko's at-bat in the fifth inning that proved to be more damaging.
"He kind of winced. That's when it caught our attention," said Gibbons, referring to when Burnett doubled over after striking out Klesko.
Still, Burnett remained in the game to face San Francisco slugger Barry Bonds, who ripped the third pitch he saw down the right-field line for a single. With that, Burnett's night ended with a slow trek to the trainer's table.
"Obviously, it was enough to bring me out of the game," Burnett said. "I'm more worried about the fact that we didn't come out on top today. That's the main thing. We'll worry about me tomorrow."