Park suffered a right hamstring strain after throwing a pitch and then winced noticeably as he hobbled to the dugout.
Park was re-evaluated by Phillies team physician Dr. Michael Ciccotti on Thursday and it was determined that he has a Grade 2 strain and will be sidelined for 2-3 weeks.
Park will remain with the club for the next two-to-three days before reporting to Clearwater, Fla., to continue his rehabilitation.
"He's been a valuable member of the bullpen," Phillies assistant general manager Scott Proefrock said. "We've got other guys out there who are capable and can step up if we need them to."
The 36-year-old right-hander is 2-2 with a 2.52 ERA in 38 relief appearances and 2-2 with a 1.84 ERA in his past 34 relief appearances.
While the Phillies have suffered a litany of injuries to their bullpen, Park remained consistent.
The Phillies are already without Scott Eyre and J.C. Romero. Clay Condrey was just activated from an oblique injury which kept him out more than two months. If Park's injury is very serious, the club could have some difficult decisions to make for its playoff roster.
However, manager Charlie Manuel dismissed the situation as being tough.
"That'll work itself out," Manuel said. "It will take care of itself. Ain't nothing tough about it."
During the spat of injuries, the Phillies have received some good news. Brett Myers has pitched very well since returning from surgery on a torn labrum. And Tyler Walker has really progressed.
Opponents have only five hits (all singles) over their past 52 at-bats against Walker. He has held opponents to a .196 average this season and had a 14-inning scoreless streak snapped on Wednesday.
"Walker has kind of worked his way in there," Manuel said. "He kind of replaced Condrey when he was hurt."
The Phillies have used 17 pitchers out of the bullpen this season with five of them going on the disabled list -- Brad Lidge, Chad Durbin, Eyre, Romero and Condrey twice. Still, the bullpen has stranded 118 of 158 inherited runners (74.7 percent), the second-highest rate in the Major Leagues behind the Cardinals.
Manuel has been forced to constantly revamp his bullpen, and it continued with Park's injury.
Is there a solution?
"Quit getting hurt," Manuel quipped.
Andy Jasner is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.