Martin Keown fears Arsenal will have to score over in Napoli if they want to go through.
The Gunners lead 2-0 thanks to a comprehensive performance at the Emirates on Thursday night.
They had chances to kill the tie in north London but let Carlo Ancelotti's side off the hook.
That's a concern for Arsenal great Keown - as is the club's dreadful away form.
He said on BT Sport: "They've got to score, it's as simple as that. They've still got to score.
"I'm concerned. They had chances to make it safe and they didn't. That's the worry.
"It will now be very interesting to see what tactics Emery employs in the away leg now.
"Does he go with the same team, we played really well tonight? Napoli didn't cash in but they may well done next week.
"So does he change things up and tighten up in certain areas?
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"It's a big call but I do feel to go through they are going to need to get a goal over there."
Keown is concerned that Arsenal are so fantastic at home but really struggle when they leave the capital.
"We've seen this season, and lately in the Europa League, that they can't rely on their away form," he said.
"The tie isn't over and Arsenal can't go to Napoli thinking it is."
