Through most of the regular season Major League Rosters are limited to 25 players but on September 1st the rosters can be expanded to up to 40 players.
The candidates to be added to the Rays roster are catcher/utility Chris Gimenez , OF Brandon Guyer , DH Delmon Young , infielder Tim Beckham , and relievers Brandon Gomes , Josh Lueke , Jeff Beliveau , and starting pitcher Jake Odorizzi .
Delmon Young  (DH/Pinch Hitter)
The Rays player likely to see the most playing time in September will be Delmon Young. Signed on August 22nd after being released by the Philadelphia Phillies he will see playing time as designated hitter against left-handed pitching and hopefully provide power off the bench.
With the Philadelphia Phillies this year he hit .261 with 8 homers and 31 RBI in 291 plate appearances. Most of his power came against right-handed pitching (7 home runs in 219 PAs) but he hit left handed pitching better posting a .286 average (18 for 72) as opposed to .254 (53 for 209) versus right-handed pitchers. Overall, his OPS (on-base% + slugging%) was .758 versus left handed pitching and only .680 versus right handed pitching.
For him to join the team he will first have to be added to the 40-man roster. There are two moves that are most likely to happen for this to occur. The first is to recall Hak-Ju Lee  from Triple A Durham and immediately place him on the 60-day disabled list. This move would cost the Rays service time and dollars but would also allow possible post-season roster flexibility as detailed by Tommy Rancel of the Process Report in his story Rays Roster Shuffling Begins This Weekend.
The Rays already have three left handed relievers in Cesar Ramos , Alex Torres , and Jake McGee  on their active roster and all 3 are under affordable contracts for 2014. Jeff Beliveau  is also a left handed reliever who has had a very good season for the Durham Bulls going 2-3 with a 2.62 ERA and striking out 76 hitters but may find that his skill set overlaps with what the Rays already have and may be the odd man out.
Chris Gimenez  (C/1b/DH)
Barring the acquisition of another catcher Gimenez should find his way to the Rays roster to serve as a 3rd catcher. This would provide Joe Maddon  the added flexibility to pinch hit/pinch run for both Molina and Lobaton in games.
Gimenez caught in 39 games for the Rays in 2012 and hit .260/.315/.330 over 109 plate appearances. He spent this season with the Triple A Durham Bulls and improved his versatility by playing 55 games at catcher 31 games in the outfield, and 7 games at 1st base. He hit .224/.350/.305 with 3 home runs in 375 plate appearances.
Brandon Guyer  (OF/Pinch Runner)
Guyer is the hard luck player of the Rays organization. Every time a spot on the roster opens up he is unavailable due to injury. After missing most of the 2012 season due to shoulder surgery he has rebounded to put up a very solid year with the Bulls. His inclusion on the roster would be to give the Rays added right handed pinch hitters off the bench as well as an extra outfielder.
In 93 games with the Bulls he has hit .304/.380/.463 with 7 homers, 6 triples, and 21 doubles in 388 plate appearances. He has also stolen 22 bases while only getting caught 3 times. During the season at Durham he has played all 3 outfield positions including 29 games in left field, 29 games in center field, and 56 games in right field.
Tim Beckham  (Utility Infield/Pinch Runner)
Beckham the former #1 overall pick in the 2008 draft may get a call up but will see very limited action. He started the season transitioning to second base but after the season ending knee injury suffered by Hak-Ju Lee  he resumed his natural position of shortstop where he proceeded to make 21 errors. After a tepid start to the season with the bat hes picked up the pace and is currently hitting .280/.343/.393 (since July 1st he has hit .297/.366/.417 ).
Beckham will not see much action with the Rays. His call up will be more of an expose him to major league life prior to the 2014 campaign when he will more than likely be one of the Rays players who will see the 25-man roster several times over the course of the season.
Jake Odorizzi  (Long Reliever/Possible 5th Starter)
Odorizzi has appeared if 5 games (4 starts) with the Rays in 2013 and has yet to record a victory. He does have a loss but his last two appearances with the big league club have been encouraging. On June 18th he held the Boston Red Sox to 1 run in 5.1 innings and on August 29th he held the Los Angeles Angels to 1 run in 5 innings.
The 5th spot in the rotation is an open competition between Jeremy Hellickson , Roberto Hernandez , and Jake Odorizzi. His role will most likely be as a long reliever in the event a pitcher doesn’t have it or has to exit early due to injury. With the Durham Bulls he made 22 starts and went 9-6 with a 3.33 ERA.
Brandon Gomes  (Low Leverage Reliever)
Gomes has already rejoined the Rays and will be utilized as a low leverage reliever out of the pen. He missed most of the season due to a side strain and in two separate stints he has appeared in 15 games posting a 5.68 ERA.
Josh Lueke  (Low Leverage Reliever)
Lueke has had several opportunities this season but has failed to take advantage. He has appeared in 14 games and has posted a record of 0-2 with a 4.91 ERA. He has struck out 19 hitters in 14.2 innings of work but has walked 10 batters. His lack of control has been the cause of his demotion each time.
While with the Bulls he has posted a 3-1 record with a 0.63 ERA. In 57.1 innings of work he has struck out 81 hitters while only walking 15.
Rays September Roster Expansion Candidates by Steve Kinsella