Bay began feeling symptoms of the illness on Friday night prior to going 0-for-3 against the Padres. He was still feeling ill when he arrived at the ballpark on Saturday afternoon, so the team's training staff sent him to a local hospital for intravenous rehydration.
Bay returned to PETCO Park in time for the game on Saturday night.
"He was just feeling week," said Pirates GM Dave Littlefield. "He may be available for pinch-hitting. It just depends on how he continues to feel.
"It's nothing that I think is serious."
Bay has appeared in 152 of the Bucs' first 154 games. Bay's streak of consecutive games played was snapped at 307 when he missed two games in August due to a strained right hamstring.
Duffy working on a new tool: Chris Duffy has been arguably the most important player in the Pittsburgh lineup during the team's second-half surge.
The Pirates have gone 23-6 when Duffy scores at least one run and 11-0 when he crosses the plate at least twice in a game.
Although Duffy has batted .373 and scored 11 runs in his last 15 games, and stolen 23 bases in 24 overall attempts, the Bucs' leadoff man is not content with his performance. Duffy had an even better stretch at the plate as a rookie last year only to start this season in a prolonged slump.
"The past month has definitely taken a step in the right direction," said Duffy. "But I'm not satisfied. There are a lot of things that I need to get better at."
As one of the fastest runners in baseball, Duffy knows that he can greatly improve his chances of getting one base consistently by better utilizing his speed. With this in mind, Duffy has been working before every game with roving instructor Rusty Kuntz to improve his bunting technique.
"[Duffy] has pretty much gone through the system and bunting hasn't been that big of a deal because he's always been a good hitter and always hit around .300," said Kuntz. "At this level, it's just another weapon, another tool that he can use, especially with his ability to hit the ball hard the other way with the third baseman playing close."
As Kuntz sees it, Duffy can open up a lot of holes in the defense by merely threatening to bunt.
"Even if he doesn't bunt and he just fakes, he gets all nine guys moving on one fake bunt," said Kuntz. "Just by showing that, you get the third baseman in your pocket. If you're able to hit the ball by him, you've got at least a base hit. And with his speed, if he gets it between the third baseman and the bag, he's got a double."
Duffy, who plans to watch videos in the offseason of former big-league speedster Brett Butler, said that he will use at least the threat of the bunt more often in the waning days of the season.
"I should definitely attempt it once a game," said Duffy. "A guy like me, I'm not going to surprise the other team. They're playing the bunt. They're playing in. It's just a matter of putting it where I want it."
And that, Duffy said, will take a lot of practice.
"Everybody is throwing sinkers and cutters now," Duffy said. "When you get a guy throwing a four-seam fastball it's rare these days. It's a little tougher to bunt."
Davis works on slide: Rookie center fielder Rajai Davis, like Duffy, has speed to burn. However, Davis has not enjoyed the same level of basestealing success as the guy in front of him on the depth chart.
Davis has been caught stealing three times in four tries. In two of those attempts, including one on Friday night against the Padres, Davis was in ahead of the catchers' throws but slid past the bag.
According to Kuntz, who worked with Davis on the field prior to the game on Saturday night, Davis' problem is that he is simply starting his slide too close to the bag.
"He just doesn't realize how fast he can run yet," said Kuntz. "He might be faster than Duffy right now. I've seen it twice now where he's slid right by the bag. He's getting that caboose down so late."
How could a player who has stolen more than 200 bases in the Minor Leagues suddenly lose track of the proper time to slide into a base?
For Davis, who has had just 12 at-bats since being recalled from Triple-A Indianapolis on Aug. 14, it's just a matter of being rusty.
"It's tough when you are not playing," said Davis. "You've got to figure out where you are on the basepath -- where you need to start your slide.
"It's like everything -- if you don't use something you lose it, or you don't stay as sharp."
Gonzalez feeling good: Pirates closer Mike Gonzalez, who has been sidelined by left elbow tendinitis since Aug. 24, threw a 45-pitch bullpen session on Saturday. After throwing only fastballs on Thursday in his first trip to the mound since the injury, Gonzalez mixed in changeups and curveballs on Saturday.
Gonzalez will throw off of the mound again on Sunday, and he expects to be activated from the disabled list when the Pirates return home for the final six games of the season.
"I haven't felt this good in about a month," Gonzalez said. "I'm definitely looking forward to Tuesday."
On deck: The Pirates and Padres will conclude their weekend series Sunday afternoon at PETCO Park at 4:05 p.m. ET. Right-hander Marty McLeary (1-0, 4.76 ERA) will make his first big-league start against right-hander Clay Hensley (10-11, 3.81 ERA).
Ed Eagle is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.