"People must not be too quick to judge Alvaro," he told the Bristol Evening Post.
"They have to remember how difficult it is to come out of the Swiss First Division into a league as competitive as the Championship.
"I would not have brought him on board unless I had faith in him and I'm sure he will do well here.
"He is the first to admit that he could have scored more goals, but he already has one and, when he gets another, more will follow.
"Alvaro is a natural finisher and I'm not worried on that account. If you look at the games he has played so far, you can see he takes up good positions and times his runs into the penalty area. He will always get chances.
"I'm confident he can handle himself in this league," he added. "Alvaro is used to playing in big games, in massive stadiums in front of big crowds and he knows what he's about.
"It's his all-round game that first attracted me to him. He doesn't just score goals, he creates them for others.
"Alvaro is a creative player with an eye for a pass and, if he's not getting in behind defences himself, he's helping his team-mates do it.
"Just look at the pass he played to put Nicky Maynard in against Blackpool the other night - not many players would have attempted it, let alone seen the opportunity."