McClain left Sunday's playoff game against the Detroit Lions due to concussion-like symptoms and did not play in the second half. He will now need to pass concussion protocol to play in this Sunday's game against the Green Bay Packers.
Cowboys coach Jason Garrett said McClain is also dealing with an injured neck, according to NFL Network.
McClain is Dallas' second-leading tackler this season with 67. The 25-year-old also has a sack, two interceptions, three passes defended and one forced fumble.
McClain is a former top-10 pick by the Oakland Raiders in 2010 and played three seasons before being released in April 2013. Five days later, he signed with the Ravens, but in May 2013 he announced his retirement from the NFL and did not play the entire 2013 season. In July 2014, the Ravens traded him to Dallas.
The Cowboys travel to Green Bay to take on the Packers at 1:05 p.m. ET on Sunday.
- Molly Geary