3B prospect Evan Longoria is on his way to St. Petersburg and will make his major-league debut Saturday.

"I'm headed that way,'' Longoria said late Friday before boarding a flight to Tampa. "I'm very excited, obviously. I hope I'm in there tomorrow."

The Rays made the official announcement after Friday's game, placing 3B Willy Aybar on the disabled list with a left hamstring strain (the ninth Rays to go on the DL and fourth since opening day) and saying he will out at least two weeks and possibly more than a month. "It's two to we-don't-know-yet,'' executive VP Andrew Friedman said. "We have to see how he responds to the treatment and really getting some time off.'' Aybar has been bothered by the injury since spring training and had played through it.

Top pitching prospect Jeff Niemann is also coming up, and the Rays confirmed that he will make his major-league debut on Sunday, starting in place of injured Matt Garza. Niemann was 1-1 with a 3.27 ERA in two starts for the Bulls after an impressive spring training.

The Rays made a somewhat controversial decision during spring training to send down Longoria with the explanation that he needed more seasoning at the Triple-A level. Though he was hitting only .200, he has gone 5-for-11 since an 0-for-14 start.

Friedman said: "Obviously we've been decimated by injuries a bit and it's not necessarily the ideal way that we wanted to call him up but we're confident in his ability to adjust at the plate and what he brings to us defensively is something that we felt was very important where we're going. We'll see what happens and reassess when Willy is ready to come back.''

Longoria did stay in the minors long enough - 13 days, two more than necessary under baseball's rules - that his eligibility for free agency, even if he doesn't return to the minors, should be delayed an extra year, until after the 2014 season.

The Rays will have to make room on the 40-man roster for Longoria before Saturday's game.