Sanchez will join the club Monday night in St. Louis, where the Cardinals open a two-game set against the Cubs.
Romero, 34, appeared in 11 games for St. Louis this year, posting a 10.13 ERA over eight innings. He has played for six teams -- the Twins, Phillies, Rockies, Cardinals, Red Sox and Angels -- over a 14-year Major League career.
In that span, he accumulated a 34-28 record and 4.15 ERA.
Sanchez, 23, was 0-2 through 14 appearances with Memphis, tallying a 6.08 ERA. But he did not allow a run or a hit in his last five appearances, and also did not allow a run during seven Spring Training appearances, while striking out 14 batters over eight innings.
Sanchez made 26 Major League appearances last season, compiling a 3-1 record with a 1.80 ERA. He struck out 35 in 30 innings, with five saves. He ended the year with 10 consecutive scoreless appearances spanning 12 frames.