SAN DIEGO — Marine Cpl. Alexander Robinson passed away early Saturday after a suitable donor could not be found for a pair-of-socks transplant, sources confirmed today.

Robinson first checked in to Naval Hospital Camp Pendleton Tuesday morning after suffering a severe ankle sprain during his unit’s annual combat fitness test, officials said. Doctors immediately placed him on an IV drip of dihydrogen monoxide and issued him a straw, as he was initially assessed as stable with strong hopes for a full recovery.

By early Wednesday evening, however, his condition worsened and he slipped into a coma. Intubating him with a steady supply of Motrin, doctors made the decision to go ahead with a pair-of-socks replacement and put him on the transplant list.

“It was a tough call,” said Navy Cmdr. Andrea Johnson, the on-call surgeon. “Being infantry, he is by default half brain-dead, and therefore technically doesn’t meet the criteria for a POS transplant. However, we were optimistic the procedure cou…