"I want to mix and match there," said Mattingly. "That's what I wanted to do from the beginning. There's been no clear-cut guy [who has] taken over the position."
Barajas is hitting .220 with eight home runs, Navarro is hitting .183 with two home runs, and Ellis .222 with no homers and the fewest at-bats of the three.
Mattingly also hinted that Rivera is just as likely to spend time at first base as in left field, where Tony Gwynn has seen increasing playing time over the past six weeks, while raising his average from .193 to .256.
"For the most part," Mattingly said when asked if Gwynn was his primary left fielder. "I like what Tony brings out there."
Mattingly did say he was considering starting James Loney at first on Friday because he is 6-for-18 against Arizona lefty Joe Saunders. He was undecided on left field.
Meanwhile, any thoughts of Casey Blake providing a right-handed-hitting option to Loney at first base have been dashed by his continued neck stiffness. A frustrated Blake, limited to catching throws at first base on Thursday, has tried injections and therapy -- with little relief from arthritis. He won't be activated when eligible on Monday.
Rivera, 33, was hitting .243, with six home runs and 28 RBIs, when designated for assignment by the Blue Jays on July 3. But he was hitting .327 against left-handed pitching, with a .909 OPS. Loney is hitting .189 with a .431 OPS against left-handed pitching.
The acquisition of Rivera on Tuesday gives Mattingly an upgrade over Marcus Thames offensively, and flexibility defensively.
"We've seen Juan play right, left, and the report we've gotten is he can play some first. So it kind of gives us ways to use him," said Mattingly. "We'll still use Tony, too."
Although Rivera was hitting .327 against left-handers and only .219 against right-handers, Mattingly said he's more than a platoon hitter.
"I've known Juan since he was young [with the Yankees], and I see him both ways," he said. "He's not a total platoon guy."
Rivera is only two seasons removed from slugging 25 homers with 88 RBIs for the Angels, who traded him and Mike Napoli to the Blue Jays in the Vernon Wells deal in January. Toronto will pick up almost all of the remainder of Rivera's $5.25 million salary.
This is the kind of acquisition the Dodgers are pretty much limited to making, in light of their uncertain financial situation.
The Dodgers excused their three All-Stars from participating in the workout. Outfielders Matt Kemp and Andre Ethier, who have homes in the area, accepted. Clayton Kershaw, Friday night's starting pitcher, not only worked out with the team, but was the first player on the field.