If the player you bet on withdraws before the first set is completed, the bet is voided. You'll receive a full refund of your stake.
After the first set is completed, any withdrawals / disqualifications don't count and the bet is settled based on tournament progression.
For instance, you have placed a bet on Carlos Alcaraz to beat Novak Djokovic at Wimbledon. Alcaraz retires due to injury in the third game of the second set. Your bet will be settled as a loss as Djokovic progresses to the next round.
More information can be found in our Terms and Conditions.