There are a few criteria to consider when compiling this list. First is the overall skill of the player. Second is the player's ability to make those around him better. And third is the amount of depth (or lack thereof) the Chargers have at the player's position.
Without further adieu, here are the five players the Chargers cannot afford to lose.
1. QB Philip Rivers – This one is a gimme. Although the Chargers have a proven backup in Billy Volek, the drop-off between Rivers and Volek is substantial. Rivers is one of the most accurate QBs in the NFL, as well as one of the game's premier leaders. Also, he has a rare rapport with WRs Vincent Jackson, Chris Chambers and Malcom Floyd that would be impossible for Volek to replicate.
NT Jamal Williams
2. NT Jamal Williams – Williams, 33, is the key cog in the Chargers' defense. He collapses the pocket; he shuts down the inside running game; and he keeps opposing O-linemen off San Diego's linebackers. Williams' presence is especially vital after San Diego exchanged veteran run-stopper Igor Olshansky for green-as-grass prospect Vaughn Martin.
3. TE Antonio Gates – The Chargers have no way to replicate Gates' production when the five-time Pro Bowler is not on the field. Brandon Manumaleuna and Kris Wilson are both H-backs known more for their blocking and special-teams play, which makes Gates as irreplaceable as they come. Gates battled through nagging injuries for most of last season, yet still finished with 60 receptions and eight scores.
4. C Nick Hardwick – Last season -- when Hardwick and LaDainian Tomlinson battled toe injuries -- illustrated just how badly the Chargers need a strong inside running game. LT was stuffed on 7.2 percent of his rushing attempts in 2008, the ninth-highest total in the NFL. The Chargers need a healthy Hardwick to erase that disturbing stat, especially now that veteran Jeremy Newberry is not in the mix.
5. FS Eric Weddle – Weddle, admittedly the most surprising player on this list, is here for a few reasons. He played extremely well over the second half of last season; he can hold his own against the run and the pass; and he is the only player on the roster capable of competently manning center field. Look for Ron Rivera to better utilize Weddle's versatility this season, especially in zone-blitz situations.
Several top players were left off because the Chargers have capable replacements waiting in the wings at their respective positions. That's the case with Shawne Merriman (Larry English), Tomlinson (Darren Sproles and Gartrell Johnson) and Quentin Jammer (Antoine Cason), among others.
Which players can't the Chargers win without? Talk about it in the message boards.
Michael Lombardo is a member of the Pro Football Writers of America and a long-time contributor to the Scout.com network. His analysis has been published by the NFL Network, Fox Sports and MySpace Sports. He has followed the Chargers for more than 15 years and covered the team since 2003.