The Basques, who finished fourth in La Liga last season, have been paired with Arsenal, Porto, Zenit or Bayer Leverkusen, but they were ultimately handed a two-legged tie against the Partenopei.
Muniain has the utmost respect for one of the most feared counter-attacking sides in Europe but he says that Athletic are more than capable of defeating Rafael Benitez's men.
"We're facing a very skilful opponent, of a really high level," the 21-year-old attacker told reporters.
"They have great players on the counter-attack; they play with this plan. We will have to be careful, but we will not abandon our style of play.
"Certainly, it's a shame to have drawn Napoli. They and Arsenal were the worst. At least there is the positive of having the return leg at home.
"We're hoping to get to play for qualification at San Mames, but it will be difficult to beat them.
"I believe that this will be a fairly even game. But we have already played against big teams last season, and beaten them.
"I'm really impatient. There's great expectation. I cannot wait to get to Naples and immediately check out the stadium."
Athletic will host Napoli at San Mames on August 27.