Liriano reached an agreement on a two-year deal worth around $14 million just before Christmas, pending a physical. Pittsburgh general manager Neal Huntington did not get into specifics about the nature of the injury, only saying the team remains in contact with Liriano.
Liriano, 29, is 53-54 with a 4.40 ERA in seven major-league seasons. He went 6-12 with a 5.34 ERA in 2012 while splitting the season with the Twins and White Sox.
Pittsburgh had penciled in Liriano to be the team's No. 3 starter behind A.J. Burnett and Wandy Rodriguez. With the left-hander's status uncertain, Pittsburgh acquired right-hander Jeanmar Gomez from Cleveland on Wednesday.