Those are the 5 teams that are likely to be unseeded in the knockout round (actually replace Panathinaikos with Club Brugge as I made an error in judging the higher coefficient between those 2 sides). It assumes that certain teams win their 3rd round matches.
At present there are 5 teams already in the knock out round, 3 seeded, 2 might be seeded, but higher ranked sides could qualify via the 3rd round yet.
The 3 guaranteed seeded sides are United, Valencia, and Bayer Leverkusen. The 2 sides in the knockout round, but their seeding status is unclear, are Sporting Lisbon and Lazio. The 3rd round ties are as follows:-
Panathinaikos V Club Brugge
Young Boys Bern V Monaco
CSKA Moscow V Sparta Prague
Rapid Vienna V Ajax
Fenerbahce V Shakhtar Donetsk
Those sides in BOLD have the higher coefficient, and were the seeded sides in the 3rd round. I've assumed they all win. If they do then CSKA Moscow and Shakhtar Donetsk will also be seeded in the knockout round, pushing Sporting Lisbon and Lazio into the unseeded pot. If one of CSKA or Donetsk fail to qualify then Sporting Lisbon would be seeded. If both fail to qualify then Ajax would be seeded. Lazio would need CSKA, Donetsk and Ajax to lose to become a seeded side, highly improbable.