PHILADELPHIA -- The Dodgers arrived at Citizens Bank Park on Monday afternoon with a roster in a state of flux. In all, they had to make five roster moves, including placing right-handed reliever Javy Guerra on the 15-day disabled list after he got an MRI on his right knee, which revealed inflammation, after Sunday's game.

The Dodgers also activated outfielder Juan Rivera, purchased the contract of reliever Shawn Tolleson from Triple-A Albuquerque, optioned Scott Van Slyke to Albuquerque and moved Matt Guerrier to the 60-day disabled list.

Guerra was hit in the face by a line drive off the bat of Atlanta catcher Brian McCann on April 28 and twisted his knee, which has proven to be more troublesome over the past 1 1/2 months.

"He'd been having the knee stuff ever since he got hit," said Dodgers manager Don Mattingly, who had yet to see the MRI report before Monday's game against the Phillies. "It wasn't as much of a concern, and we thought he could get through all that until he started saying he tried to change his mechanics a little bit to compensate and his arm was getting a little sore.

"At that point, that wasn't going to work for us. The fact he was changing mechanics was kind of dangerous. This kid has too good of an arm to be messing with that."

Worth noting

• Rivera was activated from the disabled list on Monday after he had been sidelined for a month with a ruptured hamstring tendon. He played in three Minor League rehab games last week.

• Tolleson was called up from Triple-A to replace Javy Guerra on Monday. The righty was last year's organizational Pitcher of the Year. He started this season at Double-A Chattanooga and was promoted to Albuquerque two weeks ago.

• Tony Gwynn Jr. was in the original lineup on Monday night, but the veteran outfielder was scratched due to dehydration he suffered on Sunday, the result of food poisoning and a tight hamstring.

"His hamstring got real tight yesterday," manager Don Mattingly said of Gwynn, who was available off the bench Monday. "I feel he's a little bit dehydrated today. He told me he was fine, but [trainer Sue Falsone] is worried about him being a little tight and a bit dehydrated."

• Left fielder Bobby Abreu played in his first game at Citizens Bank Park since he was traded by the Phillies to the New York Yankees on July 30, 2006.