As the 1985–86 season approached, McDonald endured questions about whether he was reaching the point where age and injuries meant he could no longer be an effective NHL player. Hoping to prove himself, he set a goal of playing all 80 games for the Flames. He succeeded, and scored 28 goals and 71 points in the process, despite dislocating his thumb in the preseason and suffering minor knee and hip injuries during the course of the year. He later said it was a matter of pride to him not to miss a game. In the playoffs, McDonald was witness to one of the most infamous mistakes in NHL history. With the score tied at two in the seventh game of the Smythe Division final against Edmonton, McDonald chased Oilers' rookie Steve Smith around the Edmonton net. Smith attempted to pass the puck forward, but inadvertently hit the back of goaltender Grant Fuhr's skate, deflecting the puck into his own net.