Player injuries are almost always accounted for in the line offered on a given game. A high-level player can impact a team’s rating by several points, causing a two- or three-point move in the line and/or total.
Lesser contributors, such as a starter, can also affect the line by a half-point to one-point, in most instances. The job of the handicapper is to determine whether or not the contribution of the new lineup will be made up in reference to the spread.
Some handicappers will just pass on games when a key player is out of the lineup, while some bettors will automatically fade (bet against) the team that is missing the key personnel.
Sometimes, teams will step up in the absence of the star player, to make up for the lack of scoring or defense. This can sometimes last for one or more games. Also, there can be value on a team that is missing a key player, especially if it is an elite team and have other players whose roles can be increased, or if there are other role players to fill in.