The 42-year-old American pulled out of Tirreno-Adriatico on stage six because of the problem and the Lampre-Merida medical staff agreed it was better to avoid racing in the cold conditions expected during Thursday's decisive mountain stage at the Volta a Catalunya. Horner finished 37th on stage three to La Molina in the Pyrenees, 47 seconds behind stage winner Joaquim Rodriguez (Katusha).
"The withdrawal will allow Chris Horner to plan a proper program of recovery and trainings with Giro d’Italia as main target: he’ll also perform some reconnaissance on the courses of the main stages," the Lampre-Merida team said in a brief note on its website.
The Italian team told Cyclingnews that Horner's Achilles problem could force him to miss the Volta a Pais Vasco (April 7-12). As an alternative he could ride the Giro del Trentino stage race (April 22-25).
Horner struggled with a knee injury in the first half of 2013 and underwent surgery in June, forcing him to miss the Tour de France. He returned to racing at the Tour of Utah and surprisingly went on to win the 2013 Vuelta a Espana, becoming the oldest ever winner of a Grand Tour.
He joined Lampre-Merida in January after struggling to find a contract for the 2014 season.