Prior, who missed the first two months of the season with a sore right Achilles tendon, was making just his eighth start of the season. He came off the disabled list June 4.
Trainer Dave Groeschner and pitching coach Larry Rothschild
quickly went to the mound and consulted with Prior before Glendon
Rusch was called in from the bullpen.
Prior gave up one hit and a run, on Geoff Jenkins' sacrifice fly
in the first inning.
The Cubs have been hit hard by injuries this season. Prior,
Kerry Wood, Sammy Sosa, Alex Gonzalez, Todd Hollandsworth, Kent Mercker, Mike Remlinger, Mark Grudzielanek, Todd Wellemeyer and Joe Borowski have all been sidelined at some point this season. Third baseman Aramis Ramirez has been out since July 2 with a groin strain.
Prior was 18-6 last season, including 10-1 during the Cubs' run to the playoffs. He was 2-2 this season before Thursday night's
Prior, 23, has been on the disabled list in each of his three
major league seasons. He hurt his left hamstring running the bases
in 2002 and bruised a shoulder last season in a collision on the
bases with Atlanta second baseman Marcus Giles.