PHOENIX – A's manager Bob Melvin remained upbeat Thursday despite news that closer Grant Balfour needed arthroscopic surgery to repair a torn meniscus in his right knee and will be sidelined four to six weeks.

Balfour had what was termed successful surgery Thursday afternoon and likely will be ready when the season starts in April.

But Melvin is aware that timetables are guidelines and nothing more. The first names Melvin mentioned to pick up the slack, should the need arise, were right-hander Ryan Cook and left-hander Sean Doolittle.

"It would be no surprise to me if Balfour was pitching in 3 1/2 weeks," Cook said. Cook is the logical choice to close if one is needed because he's right-handed and has done it before. He posted a 2.09 ERA and 14 saves in 2012.

The ninth inning, however, was something of a problem. Along with his 14 saves came seven blown saves. All four home runs he allowed came in the ninth inning, when he had a 4.72 ERA. Compare that to the 0.84 mark he had in the eighth inning, and it's clear he isn't settled in as a closer.

Balfour had 24 saves, a 2.53 ERA and just two blown saves last season. Those came during a stretch of six games in late April and early May when he gave up seven earned runs in 4 1/3 innings.

Balfour lost his job to Brian Fuentes and then Cook, and it took until mid-August before he got it back. Balfour then reeled off 17 consecutive saves to close the regular season.

Giants – Pitcher Ryan Vogelsong extended his bullpen session, throwing for several minutes after the other pitchers in his group finished.

Vogelsong is preparing to represent the United States in the World Baseball Classic.

"It's going to be so vital for us to make sure these guys are ready, and that's why his pen was a little longer," Giants manager Bruce Bochy said. "He's got to be game-ready. He feels good and looks good, and we expect him to be ready to go."

Bochy said he spoke to Team USA manager Joe Torre on Wednesday and was told Vogelsong would start the second game.

"With all he had to go through, this is an honor for him," Bochy said. "We're happy for him. It's a pretty amazing story."

• Today is the reporting date for position players, and Saturday will bring the Giants' first full-squad workout. Aside from Angel Pagan, Marco Scutaro and Joaquin Arias, all returning position players have reported to camp.

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