Dallas Cowboys offensive guard Nate Livings needs to have another surgery on his right knee, according to ESPN Dallas.
Livings underwent knee surgery in February.
He got hurt again in May, but was unable to practice Thursday.
The Cowboys are also without guard Mackenzy Bernadeau due to a hamstring injury.
So, the Cowboys have signed Jeff Olson and James Nelson as reinforcements for the line.
The Cowboys are also looking at former Kansas City Chiefs and New England Patriots offensive guard Brian Waters.
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Aaron Wlson covers the Ravens for The Baltimore Sun.