Yes, it mandatory to have a credit card to rent a car.

By mutual agreement with all the Portuguese Car Hire Companies it is essential to sign and leave a Credit Card slip to rent one of our cars.
We only accept credit cards. Prepaid credit card, virtual credit card or debit card are not accepted.
Reason:
- You are renting a car not buying, it's a movable asset, we need an guarantee and a commitment that the car will be returned to us and in the same condition as collected.
- Negligence is not covered by any extra insurance
- Electronic tolls (the tolls operator has at least 48 hours delay sending the readings)
- Road Fines
- Missing fuel
- Garage bills related with fuel mistake
- Etc