Davis, who suffered ankle and knee injuries against the Minnesota Vikings last Sunday, finishes his season with 63 tackles, three forced fumbles and two sacks. He'll be replaced in the lineup by rookie Jahlani Tavai.
Dahl, who hurt his back and knee vs. the Vikings, was in the midst of his first year as a starter at guard. He did end up in a small rotation with Kenny Wiggins, who will replace him at guard.
Davis and Dahl are the second and third starters to be placed on injured reserve this week, joining receiver Marvin Jones.
The Lions signed offensive tackle Dan Skipper and running back Wes Hills off the practice squad to take their roster spots. With starting back Bo Scarbrough listed as questionable, Hills, an undrafted rookie from Slippery Rock, could end up seeing some work with Ty Johnson and J.D. McKissic.