The Raiders, strapped by the salary cap, didn’t spend a ton of money in the free-agent market, but they signed a handful of solid veterans, most of those on defense. Here’s a look at four free agents who are likely to start for the Raiders:

CB Ron Bartell : The former St. Louis Ram looked impressive during offseason workouts and is expected to start on the left side, filling the spot that opened when the Raiders released current Kansas City Chief Stanford Routt in a cost-cutting move. Unfortunately for Bartell, he injured a hamstring while working out a week before camp opened and has yet to practice. He has continued to increase the intensity of his rehab program, and coach Dennis Allen said Bartell looks close to being ready to join his teammates on the field. Bartell played seven seasons and started 65 games for the Rams, but last year he suffered a season-ending neck injury in the opener, breaking a small bone. He said he has recovered completely from that injury, but returning to full contact will likely still pose a test -– physically and mentally.

CB Shawntae Spencer: Spencer played eight seasons and made 72 starts for the 49ers, but he has a lot to prove after a nightmare 2011 campaign. He didn’t start a single game and appeared in only nine for the 49ers in coach Jim Harbaugh’s first season. After last season, the 49ers released him. Spencer is running first team at right corner, but he has looked shaky at times. Allen said he wants to see improvement but isn’t ready to “push the panic button.” Spencer said he is still “battling” a turf toe injury he suffered last season against the Eagles.

OLB Philip Wheeler: The Raiders signed Wheeler to fill the hole on the strong side left when they parted ways with Kamerion Wimbley in another move to clear salary cap room. Wheeler, coming off a career year in his fourth season at Indianapolis, is a smaller, quicker linebacker than Wimbley, who signed with Tennessee. He should improve the Raiders’ pass defense, and he’s quick enough to blitz in the Raiders’ new, aggressive defensive scheme. Wheeler also showed his skill as a tackler last year, making a career-high 84 stops. The Raiders, however, will likely have to find someone else to fill Wimbley’s role as an edge pass rusher in the nickel defense. He had seven sacks last season and nine in 2010.

OG Mike Brisiel: The Raiders gave the former Houston Texan a reported five-year, $20 million deal, which tells you what they think of their new starting right guard. What makes Brisiel so valuable to the Raiders is his experience in Houston’s zone blocking scheme. New Raiders offensive line coach Frank Pollack was his assistant O-line coach at Houston, and new offensive coordinator Greg Knapp was the Texans’ quarterbacks coach. Knapp’s offense relies heavily on zone blocking. Brisiel is a tough, blue collar player as opposed to a dazzling physical specimen. Brisiel entered the NFL as an undrafted rookie from Colorado State. In a crucial game late last season, Brisiel played on a broken leg. That’s toughness. Brisiel has struggled at times in pass protection against the imposing defensive tackle duo of Tommy Kelly and Richard Seymour. He’s not alone.

Follow Raiders reporter Eric Gilmore on Twitter: @CBSSportsNFLOAK.