Santana will come out of the bullpen Friday against the Rockies, piggybacking the starter, Scott Alexander, MLB Network Radio reports.
Alexander is the starter, but is not expected to work more than a couple innings, as he is a reliever by trade. Santana, who has been acting as a starter in the upper levels of the minors this season, is the one who could log a starter's workload -- meaning he could still get the win if he pitches well, despite not starting. Coors Field is not an ideal place to make a big-league debut, so expectations should be tempered, but Santana has mid-rotation upside in the long term.