Santana suffered a setback with his right adductor strain Sunday while on a rehab assignment with Triple-A Reno, Nick Piecoro of The Arizona Republic reports.
Santana had appeared poised for activation from the 10-day injured list ahead of Monday's game against the Rangers, but his status is now up in the air. The 40-year-old was functioning as the Diamondbacks' primary first baseman before getting hurt in early April, but with the emergence of Ildemaro Vargas, Santana could be looking at a reduced role when he does make it back.