Dodgers outfielder Juan Rivera is out with a torn hamstring

Left fielder Juan Rivera could be sidelined for as long as two months, trainer Sue Falsone said.

Rivera was placed on the 15-day disabled list Wednesday with a left hamstring injury. Falsone revealed that he, in fact, has a ruptured tendon. Surgery hasn’t been ruled out.

Utilityman Jerry Hairston Jr. joined Rivera on the disabled list Friday with a strained hamstring. Hairston’s place on the active roster was taken by Justin Sellers, who was recalled from triple-A Albuquerque.

Hairston has a Grade 2 strain, according to Falsone. Rivera has a Grade 3 strain — that is, a complete tear.

The lack of medical literature on Rivera’s type of injury makes it difficult to forecast how long he will take to recover.

“There’s one really, really good study, but even that only has 25 people in it, and they’re not all baseball players,” Falsone said. “So we don’t have as clear an idea of how long it takes those people to get back.”

The best-case scenario is that Rivera will be ready to return soon after the Dodgers re-examine him in two weeks.

“I don’t think that’s necessarily what we’re looking at,” Falsone conceded.

If Rivera elects to have surgery, the operation would be to clean up the tendon, rather than reattach it. The tendon isn’t necessary and is often transplanted into elbows for Tommy John surgery.

But Falsone said: “We’re not at that point. We don’t know right now. We’re not on that path. It is a consideration.”

Even if Rivera has surgery, he should be back in six to eight weeks.

In Rivera’s absence, recently-added Bobby Abreu started in left field on Friday. Rookie Scott Van Slyke figures to also get some starts there.

Meanwhile, Hairston said he thinks he will be ready to play on May 22, the day he is eligible to be activated. The Dodgers waited five days to place Hairston on the disabled list, hoping he would be able to return this week.

“It got better on Monday and Tuesday, and it just stayed the same,” Hairston said. “I couldn’t get over the hump.”

Magic jerseys

The Dodgers returned from their day off to each find packages in their lockers containing two Lakers jerseys autographed by new minority owner Magic Johnson.

One had a personalized inscription. The other was to give to charity.

Tony Gwynn Jr., a Lakers fan, was particularly delighted with the gift.

“This was a nice surprise,” Gwynn said.

Gwynn said he would like another jersey signed by Johnson.

“My dad’s birthday just passed, so I’m working on getting a personalized jersey for him,” Gwynn said.

Gwynn’s father, Hall of Famer Tony Gwynn Sr., once autographed a bat for Johnson. Johnson, in turn, signed a basketball for him.

Before the game, another member of the ownership group, Stan Kasten, visited the clubhouse. He told the players of the importance of signing autographs, reminding them they could provide fans the same kind of joy they felt when they found the autographed jerseys in their lockers.

dylan.hernandez@latimes.com