Tomorrow night is the deadline to add players currently in the organization to the 40-man roster in order to protect them in the Rule 5 Draft, which will be held December 12. Currently, there are four spots available on the roster. They have already cleared some space and could clear some more (Deunte Heath and Mike McDade come to mind), if they wish.
The players who need protection are essentially: 1) those who signed in 2009 and were 18 years old or younger, and 2) those who signed in 2010 and were 19 years old or older. If a player is selected, the selecting team essentially needs to keep him on its 25-man the entire 2014 season or has to offer him back to his original team.
The most obvious is CF Trayce Thompson. While he hasn't performed to his upside yet, he's still got that potential and it's almost certain the White Sox will add him. He would be a difficult guy for a selecting team to carry the entire season due to his offensive limitations but he's a plus defender in all three outfield spots and his upside would make him very attractive.
The next likeliest is INF Carlos Sanchez. While his weak 2013 performance halted his meteoric rise, he's a player with a near-certain major league future. A selecting team could easily carry a defensive whiz such as him on its roster and his bat may well be developed enough to be passable at the major league level.
OF Brandon Jacobs is one the White Sox will seriously consider adding. Similar to Thompson, he's a guy with lots of tools. But I'd rate him as significantly less likely to ever put them together to be a legit major leaguer and he also can't play center. There's less danger a team would select him but the White Sox may think highly enough of him not to risk it.
Catchers can make good Rule 5 picks because the offensive bar is set very low for them and a good defender with upside is something a team can carry. The White Sox have a couple catchers who would be eligible - Michael Blanke and Miguel Gonzalez. Gonzalez is the one with a good defensive reputation and the White Sox outrighted him after the season, so they obviously aren't too concerned with losing him. For an offense-first catcher, Blanke hasn't really done much to live up to that reputation so he's unlikely to be protected or be a be a great loss if picked.
INF Tyler Saladino is another long-shot. He leaped up prospect rankings after a couple very solid campaigns in A-ball and then during 2012 spring training had the rather unique honor of being called into major league camp after impressing Robin Ventura. His past two seasons, mostly in Birmingham, have been extremely poor offensively and he doesn't get much attention anymore. Still, he can play credibly up the middle and perhaps another team would be interested.
Pitchers are very popular as Rule 5 picks but the White Sox don't have anyone of note who requires protection. LHP David Purcey re-signed with the White Sox on a minor league deal and isn't on the 40-man so he is eligible but unlikely to be picked.
3B Alex Liddi also signed a minor league deal and isn't on the 40-man so he, too, is eligible. Liddi had multiple MiLB contract offers so perhaps one of the spurned teams will do what the White Sox did with Angel Sanchez in last year's draft. No big loss if they do.