Halladay was roughed up Sunday by the Miami Marlins in a 14-2 defeat, his second poor outing in a row. After the game, the two-time Cy Young Award winner acknowledged he has been pitching with a sore shoulder. He said he will have tests this week in Los Angeles and be examined by Dr. Lewis Yocum.
"It's not something that I had before," Halladay said. "It's something new this year. I felt good all spring. I had soreness in there and just wasn't able to get rid of it."
Halladay, who turns 36 this month, made a statement but did not take questions from reporters. He has struggled through seven starts this season, going 2-4 with an 8.65 ERA.
The right-hander said he started feeling discomfort the morning after an April 24 outing against Pittsburgh. He has made two ineffective starts since.
"I woke up and didn't really think anything of it, just regular soreness," Halladay said. "It has kind of progressed over the last two weeks or so."
Phillies general manager Ruben Amaro Jr. said the team's former ace will likely be placed on the disabled list.
Miami rookie Adeiny Hechavarria hit a grand slam and a bases-loaded triple off Halladay, who had his worst start since his own rookie season with Toronto in 1999.
The eight-time All-Star left after giving up nine runs on four hits, four walks and two hit batters in 2 1-3 innings. He also threw a pitch behind a batter.
Halladay (2-4) has given up at least five earned runs in four of his seven starts this season.
"I have a hard time watching him struggle," Phillies manager Charlie Manuel said. "Usually when he's on, he has great location. That's the kind of pitcher he is."
Kevin Slowey (1-2) pitched seven shutout innings for his first win since September 2010. He allowed two hits while striking out seven and walking two.
Slowey had been winless in 22 major league appearances, including 15 starts. His previous victory came on Sept. 18, 2010, as a starter for the Minnesota Twins.
"I'm really thankful for the opportunity to get a win," Slowey said. "When you don't have a win since 2010, you're thankful to still get the ball every fifth day."
Hechavarria tied a club record with seven RBIs.
Justin Ruggiano homered twice off Philadelphia relievers, and rookie Marcell Ozuna went 3 for 4 with two doubles and three RBIs for the Marlins, who set a season high for runs. The output by the league's worst offense was surprising - especially against Halladay.
"To jump on Halladay like we did was big," Miami manager Mike Redmond said. "We were able to capitalize on his mistakes. He didn't look like the same guy we've seen over the years. He usually doesn't make mistakes."
Halladay, who has the most complete games (67) and shutouts (20) of any active pitcher, had 35 wins since Slowey's last one. But he hasn't resembled that pitcher for most of this season. Following Tuesday's poor outing in which he allowed eight runs on nine hits in 3 2-3 innings of a 14-2 loss to Cleveland, Halladay continued the troubling trend against Miami.
The Phillies have been outscored 28-4 in his last two starts.
Halladay helped the Marlins in the first with three walks and a hit batter. With the bases loaded, Ozuna put Miami on the board with a two-run double. Umpires reviewed the play to see if it was a home run but upheld the call on the field that the ball hit the top of the wall. After Halladay walked Greg Dobbs to load the bases again, Hechavarria, who entered batting .169, cleared them with a triple to right.
After a 1-2-3 second inning that featured two strikeouts, Halladay's struggles resumed in the third. He opened the inning by hitting Ruggiano with a pitch for the second time in the game. It was the fourth hit batter of the season for Halladay, who plunked just five per season over the last four years in an average of 220 innings. He also threw behind Ozuna later in the inning.
A walk to Ozuna and a single by Dobbs loaded the bases with nobody out. After Miguel Olivo struck out, Hechavarria hit a grand slam just over the wall in right to give Florida a 9-0 lead and chase Halladay.
"We got beat up pretty bad," Manuel said. "He just didn't have his command today."
Hechavarria's drive was first ruled a double but umpires reversed the call after reviewing the replay.
Halladay exited to a mixture of boos and cheers, though the majority of the crowd politely applauded. The nine earned runs were the second-most of his career, topped only by the 11 he gave up as a rookie with Toronto in a 17-1 loss to the Angels on April 29, 1999.
Meanwhile, the Phillies' hitters continued to have their own problems. A night after managing only one hit off 20-year-old rookie Jose Fernandez in a 2-0 loss, Philadelphia had just four against Slowey and relievers A.J. Ramos and Jon Rauch.
"We have trouble scoring runs, plus hitting the ball consistently," said Manuel, whose team avoided its sixth shutout with a pair of eighth-inning runs. "We're going to struggle until we start hitting the ball better, start making better contact and doing things right."
Amaro also weighed in on Philadelphia's tepid offense.
"They need to swing the bats better," he said. "It's not good enough. I believe in these guys still. I think they're good hitters; they're just not hitting the ball well. They need to do better for us to be contenders."