The Portuguese media claim Newcastle United and Sevilla are showing a strong interest in the Guinea-Bissau born front-man.
Balde is one of the top-scorers in Portugal this season with eight goals from 14 starts.
The 21-year-old - who is a Portuguese youth international - began his career with Sporting before joining Vitoria last year.
Mendes now says that there is interest in one of his prized assets.
"Some foreign clubs do want Amido Balde, but we are calm," he told Abola.
"This is a subject we will have to look closely as a club, but we have no agreement with anyone."