CHICAGO -- Former Chicago Bears linebacker Nick Roach signed a four-year, $13 million contract with the Oakland Raiders that included a total guarantee of $5 million, according to documents obtained by ESPNChicago.com.

Roach received a $3.185 signing bonus when he signed with the Raiders on Friday.

The Bears were given an opportunity to match the deal, but declined, according to a league source.

Roach is expected to man the middle of the Raiders defense next season, although he primarily lined up at strong side linebacker during his six seasons in Chicago. But Roach did an admirable job filling in at middle linebacker for Brian Urlacher late last season when he recorded 41 tackles in the Bears’ final four games.

Roach's contract currently rates as the third most lucrative deal signed by a linebacker to date in this year's free agent class, behind only Miami's Dannell Ellerbe and Phillip Wheeler. Another ex-Bears linebacker, Geno Hayes, signed a two-year, $2 million deal with the Jacksonville Jaguars.