Whom might Manchester United draw for the UEFA Champions League knock-out stages?

The group-stages for the 2012/2013 UEFA Champions League has just concluded and the picture has become more clear on whom Manchester United might draw for the first-round of the knock-out stages. The rules are pretty clear: The eight group winners will be matched up against against a second-place team that is not from their own group-stage group and United cannot draw an English side for the initial knock-out stage round. The draw will occur on December 20. Another draw will occur for the quarter-final and semi-final knock-out rounds after this initial knock-out round concludes. These are two-legged ties to occur in early February -- with away goals being the tiebreaker -- and United will host the second of these games at Old Trafford. Here are the six clubs that United could potentially be matched up with:

- FC Porto (Portugal)

- AC Milan (Italy)

- Real Madrid (Spain)

- Shakhtar Donetsk (Ukraine)

- Valencia (Spain)

- Celtic (Scotland)

Quite obviously, Real Madrid is the most dangerous out of these possibilities as they are the second-favorite (behind FC Barcelona) to win the competition according to bookmakers. If they are drawn, that would mean a return to the 'Threatre of Dreams' for United great Cristiano Ronaldo.

Porto and Shakhtar Donetsk would be difficult draws as well but United would be favorites -- albeit, it could be slight -- versus either side. The former has the electrifying James Rodriguez -- a player United have reportedly scouted extensively as of late -- and United fans could get a good look at the attacking-midfielder. Shakhtar are a dangerous side as they outclassed Chelsea FC over their two legs. The Ukrainian side play with tremendous cohesion and understanding while they attack with pace and precision.

Milan and Valencia could be tricky draws but United would be clear favorites against both. Despite the Italian giants showing improved form as of late, they are likely at their weakest point in two decades due to financial constraints. Valencia are in shambles in La Liga this season -- following three successive seasons of finishing third in league -- but they have good technical players and they could be improved by February.

Celtic are the 'Cinderella' team of the competition and they have a famous victory scalp from their defeat of Barcelona this season. They are, though, the clear weakest side out of the six teams United could draw.

Which teams do you hope United draw? Which teams do you hope United avoid? Feel free to offer your opinion in the poll below and in the comments section?