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2/7/2013 1:38 P.M. ET

Minor Leaguer Arnett undergoes knee surgery

MILWAUKEE -- Eric Arnett, the Brewers' seemingly star-crossed former first-round Draft pick, underwent knee surgery on Thursday that will sideline him for most or all of 2013.

Dr. William Raasch repaired a torn ACL in Arnett's right knee, a procedure expected to sideline the right-hander for 5-6 months. In opting for surgery, Raasch, the Brewers' head physician, concurred with Reds physician Dr. William Kremchek, who had examined Arnett earlier after the pitcher injured his knee while running.

It's a stroke of bad luck for a player who was just showing signs of promise after years of frustration.

Arnett, 25, was the 26th overall pick in the 2009 First-Year Player Draft out of Indiana University but experienced a drop in velocity after reaching the professional ranks, and is 8-19 with a 5.30 ERA in four Minor League seasons. But those numbers include a relatively successful conversion to relief in 2012 at Class A Brevard County, where Arnett posted a 3.56 ERA and held right-handers to a .224 batting average over 33 appearances.

"He was much better. There was some optimism there," Brewers assistant general manager Gord Ash said earlier this week. "In short spurts, he appeared to be more comfortable, so this is definitely a setback. But [after surgery], he will just have to get geared up for instructional league and make up for lost time."

Arnett has not lived up to his first-round billing so far, but it is worth noting that the '09 Draft otherwise has borne fruit for the Brewers. Supplemental first-round pick Kentrail Davis, one of the extra picks Milwaukee received after CC Sabathia departed via free agency, is a non-roster invitee at Spring Training camp, while third-rounder Josh Prince, sixth-rounder Hiram Burgos, seventh-rounder Khris Davis, 16th-rounder Scooter Gennett and 22nd-rounder Mike Fiers are all on Milwaukee's 40-man roster.

Fiers made a big splash in 2012 with the big league club, going 9-10 with a 3.74 ERA in 23 appearances, including 22 starts, and is a contender for a spot in the team's 2013 pitching rotation. Burgos was 10-4 with a 1.94 ERA for three Brewers affiliates in 2012, including eight starts at Triple-A Nashville in which he posted a 2.91 ERA and won the organization's Minor League Pitcher of the Year honor.

Gennett ranks No. 7 on MLB.com's new list of the Top 20 Brewers prospects, just updated this week. Burgos is No. 13 on that list, and Khris Davis is No. 16.

Adam McCalvy is a reporter for MLB.com. Read his blog, Brew Beat, and follow him on Twitter at @AdamMcCalvy. This story was not subject to the approval of Major League Baseball or its clubs.