How the 40-man Roster works:

"Each Major League Baseball team maintains both a 25-man roster and a 40-man roster of players. Players on the 25-man roster are eligible to play in official major league games throughout the season. The 40-man roster includes the players on the 25-man roster plus as many as 15 players who are either on the team's 15-day disabled list or who are in the team's minor league system.

From September 1 through the end of the regular season, any player on the 40-man roster (also referred to as the "expanded roster") is eligible to play in an official regular season game. Many young players make their Major League debuts in this way, as "September call-ups". Players must be on a team's 25-man roster as of August 31 to be eligible for post-season play. The only exception is that a player on the 60-day disabled list may be replaced by another player from the team's 40-man roster (as of August 31) who plays the same position."

The two most likely players to be dropped to add a player, could be Dusty Ryan and possibly Lance Zawadski or even Steve Garrison. I believe Lance would be picked up if he were exposed. The Padres will call up Cory Luebke (baring any set backs or injuries) to help with the younger pitchers "work loads".  Another factor to take into consideration in regards to a potential call up in September, when the Padres expand the roster from 25-40 if the player is on the 40 man or not, if the player is on the 40 man they do not have to place a player through unconditional waivers, which would expose that player to any team.

Players that would likely be called upon could be luis Perdomo, Cesar Ramos, and Oscar Salazar whom would be brought back IF healthy. Adam Russell, despite his mediocre performance in AAA. Aaron Cunningham played very well with his brief stint at the big league level and will be one of the more probable candidates along with Luis Durango used primarily as a pinch runner.

The Padres have so many outfield candidates that it is hard to imagine the Padres adding anyone (OF) to the 40 man to lose another player, but one exception could be Wily Mo Pena. Wily Mo is annihilating AAA. Liz. Steve Garrison, Aaron Poreda and even Craig Italiano are possible candidates. Even though Porada has struggled with his command, (to say the least) he could be used as a situational lefty out of the pen to save the other pitchers such as Luke Gregerson, Heath Bell, and Mike Adams. 

Ryan Webb will also be back. It just goes to show you the domination and depth when a pitcher such as Ryan Webb is elected to be sent down instead of the rookie Ernesto Freri because of his sucsess, and flat out domination of opposing batters.  People have asked about Josh Barfield and Nick Green, the only problem with either of those two players is they are not on the 40 man roster and the Padres would have to drop someone to add the middle infield utility players with MLB experience.

Padres 40-Man Roster

#	Pitchers	B/T	Ht	Wt	DOB
37	Mike Adams	R-R	6'5"	195	Jul 29, 1978
21	Heath Bell	R-R	6'3"	250	Sep 29, 1977
26	Cesar Carrillo *	R-R	6'3"	170	Apr 29, 1984
29	Kevin Correia	R-R	6'3"	200	Aug 24, 1980
39	Ernesto Frieri	R-R	6'2"	200	Jul 19, 1985
27	Jon Garland	R-R	6'6"	210	Sep 27, 1979
64	Steve Garrison *	S-L	6'1"	185	Sep 12, 1986
57	Luke Gregerson	L-R	6'3"	200	May 14, 1984
52	Craig Italiano *	R-R	6'4"	215	Jul 22, 1986
38	Mat Latos	R-R	6'6"	225	Dec 9, 1987
49	Wade LeBlanc	L-L	6'3"	200	Aug 7, 1984
65	Radhames Liz *	R-R	6'2"	185	Oct 6, 1983
45	Edward Mujica	R-R	6'2"	215	May 10, 1984
59	Luis Perdomo *	L-R	6'0"	170	Apr 27, 1984
44	Aaron Poreda *	L-L	6'6"	240	Oct 1, 1986
34	Cesar Ramos *	L-L	6'2"	205	Jun 22, 1984
33	Clayton Richard	L-L	6'5"	240	Sep 12, 1983
55	Adam Russell *	R-R	6'8"	255	Apr 14, 1983
46	Tim Stauffer	R-R	6'1"	205	Jun 2, 1982
54	Joe Thatcher	L-L	6'2"	230	Oct 4, 1981
58	Ryan Webb	R-R	6'6"	215	Feb 5, 1986
32	Chris Young 60-day DL **	R-R	6'10"	280	May 25, 1979
#	Catchers	B/T	Ht	Wt	DOB
4	Nick Hundley	R-R	6'1"	205	Sep 8, 1983
11	Dusty Ryan *	R-R	6'4"	220	Sep 2, 1984
8	Yorvit Torrealba	R-R	5'11"	200	Jul 19, 1978
#	Infielders	B/T	Ht	Wt	DOB
10	Matt Antonelli 60-day DL **	R-R	6'0"	205	Apr 8, 1985
1	Everth Cabrera	S-R	5'10"	175	Nov 17, 1986
22	David Eckstein 15-day DL *	R-R	5'7"	175	Jan 20, 1975
23	Adrian Gonzalez	L-L	6'2"	225	May 8, 1982
15	Jerry Hairston Jr.	R-R	5'10"	190	May 29, 1976
7	Chase Headley	S-R	6'2"	210	May 9, 1984
10	Miguel Tejada	R-R	5'9"	210	May 25, 1974
2	Lance Zawadzki *	S-R	5'11"	195	May 26, 1985
#	Outfielders	B/T	Ht	Wt	DOB
88	Kyle Blanks 60-day DL **	R-R	6'6"	270	Sep 11, 1986
28	Aaron Cunningham *	R-R	5'11"	205	Apr 24, 1986
13	Chris Denorfia	R-R	6'0"	205	Jul 15, 1980
3	Luis Durango *	S-R	5'9"	160	Apr 23, 1986
18	Tony Gwynn 15-day DL *	L-R	5'11"	195	Oct 4, 1982
12	Scott Hairston	R-R	6'0"	195	May 25, 1980
47	Ryan Ludwick	R-L	6'3"	220	Jul 13, 1978
14	Oscar Salazar 15-day DL *	R-R	6'0"	195	Jun 27, 1978
16	Matt Stairs	L-R	5'9"	200	Feb 27, 1968
25	Will Venable	L-L	6'2"	210	Oct 29, 1982