Santiago was granted his unconditional release by the Tigers on Tuesday.
Santiago was reassigned to the Tigers' alternate training site Monday.
Santiago will be a part of the Tigers' 60-man player pool this season.
Santiago could make the Tigers' roster as a long reliever whenever the regular season is able to begin, Chris McCosky of The Detroit News reports.
Santiago is competing for one of the Tigers' final bullpen spots to begin the season, Chris McCosky of The Detroit News reports.
Santiago agreed Wednesday with the Tigers on a minor-league contract that includes an invitation to major-league spring training.
Santiago allowed seven runs on nine hits and three walks while striking out eight over four innings in Tuesday's 11-0 loss to the Tigers. He did not factor in the decision.
Santiago will serve as the primary pitcher Tuesday against the Indians, James Fegan of The Athletic reports.
Santiago is slated to start Tuesday's game against the Indians.
Santiago has been confirmed as the White Sox's starter for Saturday's game against the Angels.