The Padres needed to make room for the addition of first baseman/outfielder Tommy Medica and reliever Troy Patton, who was obtained Saturday from the Orioles.
Buckner's stay in San Diego was short -- like one-day short -- as he was added to the roster Saturday and started against the Cubs, allowing three runs on six hits in 5 2/3 innings in a loss.
Boyer tossed two scoreless innings of relief Thursday against the Cubs. It was his first Major League appearance since 2011 when he was with the Mets.
With Thursday's off-day, the Padres won't need a fifth starter until they return home to face the Pirates on June 2. That means Ian Kennedy, who started Sunday against the Cubs, will likely start Friday when the Padres face the White Sox in Chicago.
Medica, who began the season with the Padres, hit .161 in 31 at-bats with the team before he was sent to El Paso last month. Since then, he's hit .213 with three home runs and 18 RBIs in 89 at-bats there.