MESA, Ariz. -- For a few moments Sunday, the Giants feared the worst.

Matt Cain, the ace of the Giants' pitching staff and their Opening Day starter, avoided serious injury after being struck on the right knee by a ball hit by Alfonso Soriano of the Chicago Cubs.

"It feels fine," Cain said. "It'll probably just be stiff."

Cain added that he expects to make his next scheduled start Thursday against Seattle.

"There shouldn't be any problem with that," he said. "I just have to see what [the athletic trainers] tell me."

Cain and the Giants had to consider themselves fortunate, given a mishap that occurred elsewhere at almost the same instant. In Tampa, Fla., Curtis Granderson of the Yankees was hit on the right forearm by a J.A. Happ pitch, sidelining the slugger for 10 weeks.

Cain, who read an account of Granderson's mishap shortly before addressing reporters, acknowledged that players face the same risks during the exhibition season that they would during more meaningful junctures of the season.

"You have to go through Spring Training full-bore," he said. "... It's just kind of part of the game."

With runners on first and second and one out in the first inning, Soriano smashed Cain's 0-1 curveball up the middle. The ball struck the outside of Cain's right knee and caromed into foul territory. Manager Bruce Bochy and head athletic trainer Dave Groeschner rushed onto the field to check on Cain, who remained on his feet.

Cain said that he weathered the "the initial shock" that comes with suddenly being hit by a object.

"It takes just a little bit to get the feeling back," he said. The pitch to Soriano, Cain observed, "didn't do a whole lot."

Cain and Soriano gestured to each other shortly before play resumed.

"I'm happy he's OK," Soriano said. "I was just trying to make contact. The best thing is he's OK -- that makes me happy."

Following the brief delay, Cain received a test on his first pitch when former teammate Nate Schierholtz hit a slow chopper to the right side. That forced Cain to cover first base, which he accomplished without discomfort.

"That's the way it always goes," Cain said.

One out away from escaping the inning, Cain threw a 2-1 fastball that Dioner Navarro pounded for a three-run homer. Cain insisted that his knee didn't impede his ability to push off the pitching rubber and apply force to his delivery.

"It'd be more [a matter of] not executing the right pitch," he said.

Cain finished the inning after yielding four hits and four runs. Staying in the game, he said, wasn't an issue for debate. Nor did Cain protest leaving the game after one inning.

"They know how I am. They know I don't want to come out," he said. "But I know that it's Spring Training and it's early and I don't want to do anything to [make the injury] linger on the rest of spring."

Cain threw approximately 20 pitches and would have began the second inning were it not for Soriano's comebacker.

"We were a little concerned that maybe the knee would start swelling a little bit," Bochy said. "We didn't want to risk him landing on it funny and injuring it more."

All of the runs Cain surrendered were unearned, due to first baseman Brandon Belt's throwing error on an attempted forceout at second base one batter before Soriano's plate appearance.

Cain, who finished with a team-best 16-5 record and a 2.79 ERA last year, remained on course to start the Giants' April 1 regular-season opener at Los Angeles.