Santos was recalled by the Giants on Thursday, Susan Slusser of the San Francisco Chronicle reports.
Santos was added to the 40-man roster in November to protect him from the Rule 5 draft, but he was unable to break camp with the major-league club. Although the right-hander hasn't pitched above Low-A, he'll now be available to make his big-league debut against the Marlins' lineup, which has plenty of right-handed hitters. Santos is unlikely to pitch in high-leverage situations for the Giants.