I apologize for the title, I could not find a better one, I am open for suggestions.

Let $M$ be a smooth manifold of dimension $n$, and let $U$ be a smooth manifold with boundary, of the same dimension $n$, embedded in $M$.

The embedding induces maps on $\pi_1$.

If $\pi_1(\partial U) \to \pi_1(M)$ is injective, does this imply that $\pi_1(U) \to \pi_1(M)$ is injective?

If true, can you direct me to a reference or a short proof?

Thanks