The Welsh outfit takes on the Italian high-flyers in Naples with all to play for after a goalless draw in last week's opening leg at the Liberty stadium.
"Napoli are favourites," Hernandez said. "They play at home, we don't have an advantage heading into the game.
"We were better in the first leg but they are favourites.
"Napoli have played in the Champions League this season, they are a big team but we have a chance.
"I think we can win this game."
The Swans, coached by Garry Monk, go into the encounter on the back of another inspiring performance.
They lost 4-3 at Liverpool in Sunday's Barclays Premier League and are 12th in the standings.
Hernandez continued: "The team has come here with confidence.
"We haven't won our recent games but from our confidence standpoint, those performances were good for us.
"We had a good game in Swansea against Napoli. We played well, controlled possession and we had our chances.
"But in football, if you don't score you can't win."
Swansea will have plenty of motivation to succeed, according to the Spaniard.
He added: "It's a historic game for the club. It's always special to play in Europe.
"This game is for the players, the club and our fans to enjoy.
"We have to enjoy this moment because to play against a big team in Europe doesn't happen often."
Hernandez is hopeful his experience will help Swansea succeed against Napoli.
The Spanish midfielder got a taste of the European competitions during his playing career at Valencia.
"I've played a lot of games in Europe against big teams," he said. "I've played in the Champions League two years but for me the game against Napoli is a special game.
"I think I can make a contribution and help the team win."