no está seguro de

is not sure about

→ no

phrase Rare #33,235

is not sure about Used to express uncertainty. It can be followed by a noun, de si plus a question clause, or de que plus a statement. The form changes with the subject: no estoy seguro de, no estás seguro de, etc.

SP: Tom no está seguro de la respuesta.

EN: Tom isn't sure about the answer.

Tom no está seguro de qué decir.

Tom isn't sure what to say.

Él no está seguro de querer hacerlo.

He isn't sure he wants to do it.

No está seguro de los detalles.

He isn't sure about the details.

— El imperio de las sombras (2016)

Usted mismo no está seguro de que lo visto allí no fue una alucinación.

You yourself are not sure that what you saw there was not a hallucination.

— Solaris (1972)

Tom no está seguro de la respuesta.

Tom isn't sure of the answer.

Tom no está seguro de si Paul es un buen partido para su hija Mary.

Tom isn’t sure whether Paul is a good match for his daughter Mary.

Tom aún no está seguro de si irá o no.

Tom still isn't sure whether he'll go or not.

Tom no está seguro de donde ha ido Mary.

Tom isn't sure where Mary has gone.