Lamb, a left-hander who was the team's fifth-round pick in 2008, was a promising prospect before undergoing Tommy John surgery in 2011. Lamb made progress last season at Triple-A, throwing 138 1/3 innings while going 8-10 with a 3.97 ERA.
The Royals now have 58 players in camp, including 19 non-roster invitees.
Jeffrey Flanagan is a reporter for MLB.com. Follow him on Twitter at @jflanagankc. This story was not subject to the approval of Major League Baseball or its clubs.