Why Celtic must beware of Norwegians bearing toothbrushes, negotiating the winter break and the tenacity of Leicester's opponents Randers.
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Celtic take on a Bodø/Glimt side that demonstrated their threat by dismantling José Mourinho's Roma during the group stage. Leicester also face Scandinavian opponents who are among eight sides that must find a way to hit the ground running following the winter break.
Enterprise Rent-A-Car presents UEFA.com's guide to the stand-out stories.
Thursday 17 February
The second legs take place a week later, on 24 February.
What to look out for?
Celtic: Beware of Norwegians bearing toothbrushes
Question: which team consigned José Mourinho to the heaviest defeat of his garlanded managerial career? The heavyweights of English, Italian or Spanish football? Maybe one of the Portuguese giants back in the early days? None of them. It was Bodø/Glimt, who overwhelmed his Roma side 6-1 during the group stage.
The Norwegian side from the Arctic Circle famous for bringing novelty toothbrushes to games have enjoyed a meteoric rise, claiming the last two Eliteserien titles after none in their previous 103 years in existence. And it is not just results but the manner of them; Kjetil Knutsen puts the onus heavily on attack. Celtic be warned.
Leicester's never-say-die opponents
Randers have struggled with consistency this season but their battling qualities mean that Leicester's opponents are always in with a chance. The Danish side twice came from behind to draw with both AZ and Jablonec during the group stage, their tenacity exemplified by Simon Piesinger. The Austrian has played every minute, made a competition-high 41 clearances and chipped in with two goals from defence.
Fresh legs vs thick of it
Coaches in some countries have longed for a winter break, promoting the importance of meaningful rest as a way to guard against fatigue injuries and increase competitiveness at the business end of the season.
Play-off teams from Austria, Azerbaijan, Czech Republic, Denmark, Norway and Serbia all have winter breaks (six of the ties feature a side with a winter break against an outfit without). But they face a different challenge: how to get their players up to speed for pivotal European games with few or no competitive games under their belts?
Who is through to the last 16?
AZ Alkmaar (NED)
17 & 24 February: Knockout round play-offs
25 February: Round of 16 draw
10 & 17 March: Round of 16
18 March: Quarter-final & semi-final draws
7 & 14 April: Quarter-finals
28 April & 5 May: Semi-finals
25 May: Final (National Arena, Tirana)