The NFC-East leading Cowboys will have to take on the Patriots without a key part of their defense.

It was announced Friday that Pro Bowl linebacker Leighton Vander Esch will be sidelined for Sunday’s contest in New England due to a neck injury, and his absence could be longer than one game. The decision was reportedly made after seeing the results from a MRI exam that he took on Thursday.

The plan is for Vander Esch, who is listed as week-to-week, to have another MRI in three weeks.

“Leighton was having some symptoms. We determined [he] has some issues with his neck,” Dallas coach Jason Garrett told reporters Friday. “Won’t play this week. We don’t think it’s career-threatening.”

The injury apparently flared up in practice. He suffered a stinger, a common nerve injury of the neck and shoulder especially seen in football, during Dallas’ Oct. 20 win over the Eagles. After the Cowboys’ bye week, Vander Esch didn’t play against the Giants on Nov. 4.

The 6-foot-4 linebacker did start the past two games against the Vikings and Lions, and he totaled 10 tackles. Vander Esch alluded to dealing with more than just a stinger last week and dealt with a back injury during the Cowboys’ 28-24 loss to the Vikings on Nov. 10.

Vander Esch is an integral part of Dallas’ defensive core. He’s second on the team behind Jaylon Smith with 72 tackles, and he’s recorded half a sack, two tackles for loss, three quarterback pressures, a forced fumble and three pass deflections this season.

The Cowboys will look to veteran Sean Lee at weakside linebacker in Vander Esch’s absence. Joe Thomas, who missed two practices this week because of an illness, will likely move into Lee’s spot on the strong side if he’s healthy enough to do so.