OAKLAND -- Right-hander Santiago Casilla will undergo surgery to remove a cyst in his right tibia Tuesday afternoon at Stanford Hospital.
Casilla hopes to return to action soon after the All-Star Game. He said the discomfort is just below the knee and that he has been pitching with it for about a year.
After getting at least three separate opinions, Casilla decided to have the surgery and clear things up. He said the discomfort altered everything about his pitching routine.
Giants manager Bruce Bochy said left-hander Jeremy Affeldt will assume most of the eighth-inning responsibility, while right-handers Chad Gaudin and Jean Machi will be in the mix for the seventh and eighth innings.
Giants send down Rosario; Surkamp to 60-day DL
OAKLAND -- Right-hander Sandy Rosario was optioned to Triple-A Fresno after Monday's 4-1 loss to the Oakland Athletics to make room for left-hander Michael Kickham, who will make his Major League debut Tuesday when he starts vs. the A's.
Rosario appeared in four games with the Giants, including a scoreless eighth against the A's on Monday. He's 1-0 with a 6.75 ERA.
Left-hander Eric Surkamp, recovering from left elbow surgery, will be moved to the 60-day disabled list Tuesday to make room for Kickham on the 40-man roster.
Giants starter Madison Bumgarner said he won't necessarily seek out Kickham but if he were asked, he would tell him to "just slow down. That's what I remember when I first came here. It seemed like I was out of the game before it even happened."
Quiroz provides positive review on Kickham
OAKLAND -- Left-hander Michael Kickham was expected to join the Giants sometime Monday afternoon.
Giants manager Bruce Bochy said he didn't want to rush him and make him lose any sleep. Kickham was with the Triple-A Fresno Grizzlies in Colorado Springs when he learned he would be making his Major League debut Tuesday night, starting against the A's in Oakland.
Catcher Guillermo Quiroz worked with Kickham during Spring Training and described him as a competitor.
"He's going to compete for sure," Quiroz said. "I could see he wanted to be on the mound and to show he can pitch here."
Kickham has gone 3-1 with a 1.72 ERA over his last five starts with Fresno.
"His stuff is good," Quiroz said. "He was working on a changeup in Spring Training and has a good fastball and slider."
Bochy said Buster Posey will catch Kickham, who was drafted by the Giants in the sixth round of the 2010 First-Year Player Draft.
Kickham was 4-9 with a 5.25 ERA during his senior year at Missouri State, where he studied biology and pre-med. He struck out 103 in 96 innings.
Bochy reserving judgment on new Interleague format
OAKLAND -- Giants manager Bruce Bochy was in a good mood Monday. The commute from San Francisco went smoothly.
"It was nice," he said. "There was no traffic. We got to the bridge easily."
With two games in Oakland and two games in San Francisco, Bochy said he doesn't know how he feels about the arrangement.
"I don't know if I like it or not," he said. "I'll let you know after Thursday's game. It's like a four-game series."
• Pablo Sandoval said Monday he was still feeling under the weather but he did take batting practice for the first time in four days. Gregor Blanco was the latest Giant to come down with the "crud."
• Angel Pagan was not in the starting lineup for the second straight day but Bochy said he would be available for pinch-hitting duty Monday.
• Bochy said Marco Scutaro would assume the designated-hitter role in Tuesday's game.
Rick Eymer is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.