Bassitt was carted off the field after he was struck on the side of his head by a line drive, casting a shadow over the A's 9-0 loss to José Abreu and the Chicago White Sox.
With two on base and no outs in the second inning, Bassitt threw an 143 km/h cut fastball that Brian Goodwin drove up the middle. Bassitt went down on the mound right after he was hit, holding his head, and his teammates quickly waved to the dugout for assistance.
As players on each side looked on, Bassitt was attended to by an Oakland trainer and other personnel before he was helped into a cart while holding a towel to his face. A's centre fielder Starling Marte had his hands on his head as the right-hander was driven by him.
"Bass is conscious. He was the entire time," manager Bob Melvin said. "We don't think the eye is a problem at this point. It felt like it was below it. He's got some cuts. They had to do some stitches. He's in a scan and we'll know more about potential fractures or whatever tomorrow, or later tonight."
Melvin took no questions during his postgame Zoom session with the media, and the A's made no players available.
Abreu and Jake Lamb each hit a three-run homer for AL Central-leading Chicago, which improved to 11-11 against the AL West this year. Andrew Vaughn had two hits and two RBIs.
White Sox manager Tony La Russa called Bassitt "the No. 1 concern."
"Certainly hope that he caught a break and he's OK," La Russa said.
Lamb, who played with Bassitt last year in Oakland, said it was hard to concentrate after the play.
"It's a lot more than baseball at that point," Lamb said. "It's a friend, it's an old teammate. Any time you get hit in the head like that, it's a very scary situation."
Reynaldo López (2-0) pitched five innings of one-hit ball in his third start since he was recalled from Triple-A Charlotte last month. The right-hander has a 1.08 ERA in 11 appearances overall after he struggled last season.
Oakland's loss and the New York Yankees' doubleheader sweep against the Red Sox created a crowded picture at the top of the AL wild-card standings. The A's and Yankees are 68-52, followed by the Red Sox with a 69-53 record.
After Bassitt (12-4) left the game, Burch Smith surrendered Vaughn's two-run single before Lamb hit a drive to centre for his sixth homer.
Abreu connected against Smith in the fourth, just clearing the wall in left. With his 25th homer, the reigning AL MVP moved into a tie with Boston slugger Rafael Devers for the major league lead with 89 RBIs.
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