Castaignos joined Inter from Feyenoord in the summer, having scored 15 goals in 30 league appearances for the Rotterdam-based outfit, and has already drawn comparisons with French legend Thierry Henry.
Inter reportedly beat off competition from the likes of Liverpool, Arsenal, Real Madrid, Manchester United and Bayern Munich for the 19-year-old's signature, but the player has only featured sporadically for the Nerazzurri, struggling to force his way past Giampaolo Pazzini, Diego Forlan, Mauro Zarate and Diego Milito.
Nonetheless, Samuel believes youngsters like Castaignos are important for the future, and believes the Holland U-19 international has what it takes to succeed at the highest level.
"Our group is made up of mature players, but also of youngsters, who I hope will give their best together with us," Samuel told Inter Channel.
"We need them, and in fact, they are helping us. They're making a great contribution.
"I really like Castaignos, he moves like a true centre forward. He's difficult to mark, he's fast and he has a nose for goal.
"We just need to give him a bit more time to find his feet. He'll get better once he starts playing regularly."
Castaignos has only made three Serie A appearances for Inter so far, and is yet to net his first goal for the club.