The Royals designated Jeffress for assignment last week as one of the corresponding roster moves to make room of their roster for right-hander Guillermo Moscoso and catcher Brett Hayes.
Jeffress was one of the players the Royals acquired from the Milwaukee Brewers in exchange for right-hander Zack Greinke. Kansas City also picked up Lorenzo Cain, Alcides Escobar and Jake Odorizzi in the trade.
Jeffress barely cracked Baseball America’s top 100 prospect list entering the 2009 season. That year he struggled a bit as a starter, but was extremely impressive in 2010 once the Brewers moved him to a relief role.
Jeffress appeared in 27 games for the Royals over two seasons, posting an ERA of 5.65 with 8.2 strikeouts per nine and 7.5 walks per nine. The 25-year-old owns a career ERA of 4.31 with 10.0 SO/9 and 5.4 BB/9 over seven seasons in the minors.