Fairley, in his fourth year in the league, has not played since injuring ligaments in his knee in the team's Week 8 victory over the Atlanta Falcons in London. The "doubtful" designation indicates that he has a 25 percent chance of playing.
Fairley, 26, appeared at practice on Thursday in a knee brace but seemed to move well during the session.
The defensive tackle, who will be a free agent after this year, has recorded 14 tackles, one sack and one forced fumble in eight games this season.
The Lions also announced that wide receiver Calvin Johnson, who was limited in Wednesday's practice but participated fully on Thursday and Friday, was probable for Sunday. Defensive ends Darryl Tapp and Ezekiel Ansah were also listed as probable.
For Dallas, right tackle Doug Free, who has missed the last two games, is listed as doubtful due to an ankle injury and will likely be replaced by Jermey Parnell. Linebacker Anthony Hitchens and defensive lineman Tyrone Crawford are both listed as questionable with an ankle injury and an illness, respectively.
Detroit, 11-5 and second in the NFC North, will play the Cowboys (12-4 and first in the NFC East) in Dallas at 4:40 pm EST on Sunday.