OAKLAND -- A's third baseman Matt Chapman was missing from Monday's series-opening lineup against the Astros after developing a left knee infection.
The rookie, promoted just Thursday for his big league debut, was prescribed oral antibiotics Monday, and the A's will closely monitor his response to the medication over the next 24 hours before having a better idea of how long he'll be away from action.
"You want to wait and see how the antibiotics treat it," A's head trainer Nick Paparesta said, "and hopefully that's all we need to do."
Chapman is unsure how he acquired the infection but mentioned sliding into a fence during a game with Triple-A Nashville a couple of weeks ago.
"You're always kind of cut up and banged up from playing ball, but nothing I can put my finger on that really made me think I needed to say anything, let alone miss some time," Chapman said. "So it was kind of one of those freak things."
He had a combined three hits in his first four games, including the game-winning, two-run single in the eighth inning against the Yankees on Friday for his first Major League hit. Oakland went on to sweep the four-game set with Chapman in tow.
After Sunday's finale, he said he noticed swelling in his knee but assumed it was simply related to game actvity. He woke to more of the same Monday morning, prompting a trip to the doctor.
"Just taking it day to day," Chapman said. "Hopefully it's nothing major and I'll be back in the lineup in a few days."
Worth noting
• Shortstop Marcus Semien (right wrist surgery) is expected to begin a Minor League rehab assignment with Class A Advanced Stockton when Oakland departs for a two-city, six-game road trip following Thursday's game. Semien is expected to play in at least a week's worth of Minor League games before rejoining the A's. He had surgery April 18.
• Right-hander Kendall Graveman (shoulder) is on track to throw from flat ground by the end of the week, meaning he could be throwing off a mound as soon as this weekend.
• Right-hander Chris Bassitt, slowed in his Tommy John rehab, is back to making continued progress, with plans for him to throw a bullpen session that will include simulated game activity Tuesday. Semien will be among the hitters standing in against him.
• Reliever Ryan Dull, rehabbing a right knee strain, is running pain-free, per Paparesta, and the right-hander could potentially be cleared for a bullpen session later this week.
• Righty Andrew Triggs received a cortisone shot in his left hip Monday morning. The A's will see how he responds over the next 48 hours before determining the next course of action.