The Partenopei coach believes their Welsh opponents will put up a fight in the second leg after holding the third-placed Serie A side to a 0-0 draw at the Liberty Stadium
The Partenopei, who dropped down into the second tier of European football from the Champions League, were held to a 0-0 draw at the Liberty Stadium on Thursday in the first leg of their last-32 tie
Garry Monk's men - who are in a relegation fight in the Premier League - successfully avoided conceding on home turf in a tightly-contested game, which former Liverpool boss Benitez says he anticipated.
"I expected it would be difficult to win," the Spaniard told Mediaset Premium after the match. "Swansea are a team that dribble well and play with a fast tempo.
"We're glad we did not concede a goal and we showed that we have a good defence. We need to win the return leg to reach the next round now, though.
"It will be a perfectly weighted match because it will be a complicated game - the Welsh side will be dangerous from the start and will have quality and physical strength.
"They are also capable of waiting, playing good defensively and their three strikers using speed to attack."
The two teams clash at the Stadio San Paolo next Thursday, with the winner to face either Porto or Eintracht Frankfurt in the last 16.