A spectator was hospitalised with a serious head injury and three others were left hurt following an accident in Trier on the eve of the Rally of Germany, local police reported on Thursday.
The accident happened during a "shakedown" around the town of Konz, a trial run before Friday's timed stage, when a spectator was struck by a tyre after it flew into a crowd at 12.45 local time (1145 BST).
The spectator was airlifted to hospital with severe head injuries after being hit by the tyre from a Subaru Impeza driven by Peru's Nicholas Fox and Argentina's Fernando Mussano.
The three other spectators were left with minor injuries and the day's session was later cancelled.
The Rally of Germany, the ninth race of the World Rally Championships, starts on Friday and finishes on Sunday.