Wright was examined in the clubhouse before being taken by ambulance to the Hospital for Special Surgery. Mets spokesman Jay Horwitz said Wright had a CT scan, which was negative.
The Giants beat the Mets 5-4 in 10 innings.
Wright didn't have time to react to Cain's 0-2 pitch in the fourth inning. It hit him just above the brim of the helmet, sending it flying as Wright fell to the ground in the right-handed batter's box.
"Those are frightening moments for everybody,'' New York manager Jerry Manuel said.
Wright lay motionless on his stomach for more than a minute before trainers helped turn him onto his back. One trainer kneeled by Wright's side and talked to him. After Wright was turned over, he sat up and a trainer shone a light in his eyes.
Manuel said he didn't talk to Wright when was on the ground, but he saw ``his eyes go back and forward a bit.'' Manuel thought Wright said he was all right when he sat up.
Mets outfielder Jeff Francoeur visited Wright in the clubhouse, shortly after the All-Star walked off the field with minimal help. Francoeur said Wright made a joke from the Chris Farley movie "Tommy Boy'' about where he was hit in the head.
"He was all shook up when I came in,'' Francoeur said. "He was scared.''
Cain, who had thrown just seven balls in his first 35 pitches, walked halfway toward the plate and sat in a crouch as trainers tended to Wright. Players and managers agreed that Cain wasn't trying to throw at Wright.
Cain and Johan Santana had been locked in a scoreless matchup. Seemingly rattled, Cain gave up a run before settling down and pitching into the eighth.
"He felt horrible,'' Giants manager Bruce Bochy said. "That's the last thing he wanted to do, but he regained his composure.''
Said Cain: "It was nice to see him walk off the field. It was definitely a situation where you hoped there's no blood. I'll see if I can get a hold of him tomorrow."
Regardless of intent, Francoeur said something had to be done.
"When the third-hole hitter gets dosed in the head, you got to come back at them a little bit," he said.
And that's what Santana did.
The Mets' All-Star starter threw behind the back of Pablo Sandoval, missing him entirely in the seventh inning and drawing a warning for both teams from plate umpire Brian O'Nora.
Sandoval responded by hitting a home run, boosting the Giants' lead to 4-1. Santana then hit the next batter, catcher Bengie Molina, but wasn't ejected. Bochy came out to argue with O'Nora that Santana should have been tossed.
"He didn't think it was intentional," Bochy said of O'Nara's explanation. "That's his call.''
Wright has played in all but one of the Mets' 116 games this season, and has been a stabilizing force in a lineup ravaged by injuries. He joins Carlos Beltran, Carlos Delgado and Jose Reyes among the Mets' injured stars.
"It will be difficult for us. He has played through a number of things -- nagging injuries, fatigue," Manuel said of Wright, who didn't start Tuesday in Arizona because he had a cold. "He was going out there for us every day.''
Fernando Tatis ran for Wright and stayed in the game at third. He had an RBI single during the Mets' eighth-inning rally.
By HOWIE RUMBERG, AP Sports Writer
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