fear the worst
to expect a situation to have the worst possible result, because you know how bad the situation could be

[TahlilGaran] Dictionary of Contemporary English ▲

pessimistic expecting that bad things will happen, or that someone will be unsuccessful:
He was pessimistic about the team’s chances of winning the championship.
a pessimistic view of human nature
downbeat having an attitude that is not hopeful and not expecting success, or not expecting the situation to improve, especially the economic or political situation:
The overall mood in the stockmarket is decidedly downbeat.
The chairman made some downbeat remarks about the company’s sales performance.
His assessment of the UK’s economic prospects is generally downbeat.
gloomy not having much hope for the future:
Environmental groups are gloomy about the future of our planet.
The article painted a gloomy picture of the human rights situation in Burma.
negative considering only the bad qualities of a situation, person etc, and not the good ones:
His negative attitude towards work was affecting his colleagues.
Why are you always so negative?
fear the worst formal to expect a situation to have the worst possible result, because you know how bad the situation could be:
I hadn’t heard any news from her for over a week, and I was starting to fear the worst.
sb’s glass is half empty informal used about people who only see the bad qualities of a situation, even when other people might see better qualities in the same situation:
He’s one of those people whose glass is always half empty.

[TahlilGaran] English Thesaurus ▲

fear the worst
to feel sure that what was least wanted has happened or will happen.
When the doctor called, she feared the worst.

[TahlilGaran] English Idioms Dictionary ▲