Sanches spent the 2017-18 season in the Premier League but saw his stay with the Swans disrupted by injury and a lack of form.
The young midfielder, heralded as one of the signings of the season when his short-term move to the Liberty Stadium was confirmed, played the full 90 minutes just four times in the league.
However, Kovac, who has been unveiled as the club's new boss following the departure of interim Jupp Heynckes, believes that Sanches has the tools to be a success in the Bundesliga.
"He is a young player and you have to have understanding when he is not a hit in a foreign country immediately," he said.
"I am looking forward to working with him. He has skills which you don't see in the Bundesliga very often.
"I hope he takes this challenge here and will be a hit in the end."
Sanches has won 13 caps for Portugal and came of age at Euro 2016, when the country won the tournament, but he was left out of the squad for the 2018 World Cup, with the Seleccao losing to Uruguay in the last 16.
Kovac was also asked about the possibility of a bid for Ante Rebic, with whom he used to work at Eintracht Frankfurt.
"He is a great player, I am glad that he delivers so well at the World Cup," he said of the Croatia international. "He is a player that every team could benefit from."