Discreetly Mine, a 2010 Kentucky Derby participant who eventually became a Grade 1 winning sprinter, has been retired from racing, trainer Todd Pletcher confirmed Friday.\r\nDiscreetly Mine, a son of Mineshaft and a half-brother to the Grade 1 winner Discreet Cat, had suffered an injury to his left stifle in October, knocking him out of the Breeders&rsquo; Cup Sprint. His connections were hopeful the horse could return in 2011, but a recent re-evaluation of the injury didn&rsquo;t reveal significant healing.\r\n&ldquo;It didn&rsquo;t look like he was healing at the rate they had hoped,&rdquo; said Pletcher, who trained Discreetly Mine for Joyce Robsham. &ldquo;They felt like they couldn&rsquo;t be confident enough he would come back 100 percent.&rdquo;\r\nAs a 2-year-old, when with trainer Stanley Hough, Discreetly Mine won his second start before finishing second in the Grade 2 Futurity and Grade 1 Champagne.\r\nTurned over to Pletcher for his 3-year-old season, Discreetly Mine won the Grade 2 Risen Star Stakes at Fair Grounds before finishing fourth in the Louisiana Derby. After running 13th in the Kentucky Derby, Discreetly Mine was turned back to sprint races. After finishing second in the Grade 2 Woody Stephens, he reeled off consecutive stakes win in the Grade 3 Jersey Shore, Grade 2 Amsterdam, and Grade 1 King&rsquo;s Bishop.\r\n&ldquo;Arguably, at the end of the year, he was maybe the best sprinter around,&rdquo; Pletcher said. &ldquo;Unfortunately, he didn&rsquo;t get to compete in the Breeders&rsquo; Cup.&rdquo;\r\nDiscreetly Mine retires with a record of 5-4-0 from 13 starts and career earnings of $799,350.