"He was treated for a contusion," Giants manager Bruce Bochy said after Monday's game. "We are going to monitor him tonight and tomorrow for any concussion symptoms."
Bochy seemed relieved that Cueto appeared to avoid serious injury.
"Nothing scares me more than what happened, that line drive up the middle," Bochy said. "[Cueto's] first night game, the first pitch of the game, I'm sure he didn't recognize it off the bat. I was hoping it was what it was, more of a glancing blow. Still, it caught him pretty good."
Cueto's second start of the spring appeared destined to end immediately as Burns' line drive struck the pitcher's forehead. The ball was hit with such force that it bounded into center field, enabling Burns to record a double.
"[Cueto] thinks it nicked his glove first. I didn't see that," Bochy said.
Bochy and head athletic trainer Dave Groeschner raced to the mound to examine Cueto, who convinced them he could continue pitching.
"He was fine out there," Bochy said. "He answered all the questions. He wanted to stay out there. ... Guess it shows how tough he is, in a Spring Training game."
Cueto looked confused when the next batter, Mark Canha, dribbled a grounder between the pitcher's mound and first base. Cueto initially pursued the ball, then backed off in the belief that first baseman Brandon Belt would handle the play. Canha collected an infield single, which preceded Reddick's homer.
From that juncture, Cueto settled down, retiring nine of the final 12 batters he faced. It was the second Cactus League start for Cueto, 30, who signed a six-year, $130 million contract during the offseason as a free agent.
Chris Haft is a reporter for MLB.com. Read his blog, Haft-Baked Ideas, follow him on Twitter at @sfgiantsbeat and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.