worsen, get worse
Se piorar vou virar o ano neste assento.
If things get worse, I'll spend the New Year in this seat.
— Ирония судьбы, или С легким паром! (1976)
To make matters worse, it started to rain.
Chovia forte e, para piorar, o vento começou a aumentar.
It was raining heavily and, to make matters worse, the wind started to pick up.
Para piorar as coisas, o trânsito estava muito carregado.
To make matters worse, the traffic was very heavy.