Hudson, 26, first tore the ligament and had Tommy John surgery last July. He left the first of what was expected to be two minor-league rehab starts with elbow stiffness earlier this week. It seems likely he will require a second Tommy John surgery, which has a much lower success rate than the first procedure.
Before the injury last year, Hudson went 3-2 with a 7.35 ERA and 1.63 WHIP in nine starts. He broke out the year before, going 16-12 with a 3.49 ERA and 1.20 WHIP in 33 starts. Arizona acquired him from the White Sox as part of the package for Edwin Jackson at the 2010 trade deadline.
The Diamondbacks are 34-26 and lead the NL West by 2 1/2 games over the Giants.