As per ESPN's Jeff Dickerson;
<blockquote class="twitter-tweet"><p>Veteran RB Curtis Brinkley has passed physical and will sign a 1-year deal with <a href="https://twitter.com/search?q=%23Bears&src=hash">#Bears</a>, source confirms.</p>— Jeff Dickerson (@ESPNChiBears) <a href="https://twitter.com/ESPNChiBears/statuses/367027681239375873">August 12, 2013</a></blockquote>
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This move was necessitated by the injuries to Harvey Unga and Armando Allen.
With both Unga and Allen likely unavailable for Thursdays game with the Chargers, the Bears needed another camp body behind Matt Forte, Michael Bush, and rookie free agent Michael Ford.
Brinkley is 5'9" and 208 pounds, so I wouldn't expect him to get any fullback reps like Unga, but he'll be a veteran tailback for the coaches to evaluate.
In his three years as a pro, all with San Diego, he has appeared in 23 games with 2 starts. Last year was his most productive as a pro, with 278 all purpose yards.