Despite the low injury count among the starters, the following players went to IR for the entire 2014 season:
Raji
Barclay
R. Neal
Abbrederis
Thomas
Thornton
Tiller
I don't recall Tiller's eventual status (injury settlement?), but the other 6 counted in full against the cap as did their replacements.
Partial season IRs were:
Tretter
Robinson
Lattimore
Mulumba
All of those guys counted in full against the cap, while their replacements on the roster would have counted against the cap on a prorated basis based on weeks served.
Figuring on 6 full and 5 partial seasons missed, let's say that represents 8 replacement salaries. Even if those replacements were minimum salary rookies, that's $3.5 mil based on the current salary scale.
I would consider $3.5 mil to be the rock bottom minimum cap amount to be held for injury replacement. $5 mil is probably more like it.
So, I'd say Thompson has about $9 - $10 mil left to work with or carry over. Perhaps Pat Willis will reconsider his retirement.