35-year old righty closer Grant Balfour had knee surgery today and he will miss the next 4-6 weeks.  Balfour pitched in 75 games (0 starts) for the A’s last year and he was 3-2 with 24 saves, a 2.53 ERA and a 0.92 WHIP.  If Balfour isn’t ready for the start of the 2013 season, the A’s will turn to 25-year old righty Ryan Cook as the closer.  Cook pitched in 71 games (0 starts) for the A’s last year and he was 6-2 with 14 saves, a 2.09 ERA and a 0.94 WHIP.  At least the A’s have a capable replacement in Cook, but, they want Balfour to heal up as quick as possible.