UEFA will conduct a new Champions League last-16 draw at 2pm after a mistake involving Atletico Madrid, Liverpool and Manchester United.
UEFA said a "technical problem" was to blame and resulted in the original draw being declared void.
The issue arose when Group B runners-up Atletico were drawn and their possible last-16 opponents - all group winners - were then put into a separate pot, but United were not included.
Teams who met in the group stages are supposed to be kept apart in the last-16 draw. United did not face Atletico in the groups, but Liverpool did, and Jurgen Klopp's side were mistakenly put into the pot to potentially face Atletico - who were then drawn against Bayern Munich.
The original draw had seen United set to play Paris Saint-Germain, while Liverpool had been drawn against Salzburg.
Champions League - original last-16 draw
- Benfica vs Real Madrid
- Villarreal vs Manchester City
- Atletico Madrid vs Bayern Munich
- Salzburg vs Liverpool
- Inter Milan vs Ajax
- Sporting Lisbon vs Juventus
- Chelsea vs Lille
- Paris Saint-Germain vs Manchester United
UEFA said in a statement: "Following a technical problem with the software of an external service provider that instructs the officials as to which teams are eligible to play each other, a material error occurred in the draw for the UEFA Champions League Round of 16.
"As a result of this, the draw has been declared void and will be entirely redone."
Manchester City boss Pep Guardiola believes UEFA has made the correct decision to repeat the draw.
Speaking at a press conference to preview his side's game with Leeds on Tuesday, Guardiola said: "I think it is fair. It was a mistake but sometimes these things can happen.
"If there was a mistake you have to repeat so it is not suspicious."
How UEFA's Man Utd gaffe prompted re-draw
The Champions League draw was conducted in Nyon by UEFA deputy general secretary, Giorgio Marchetti, and UEFA head of club competitions, Michael Heselschwerdt, with the help of special guest Andrey Arshavin.
Eight balls representing eight runners-up were in one bowl, while eight group winners were in individual pots.
Every winner was to be drawn against a runner-up from a different group and football association.
Heselschwerdt confirmed that the draw process would see one runner-up drawn from the runners-up pot. A computer would then indicate which winners could be drawn against them. Balls containing the names of eligible opponents would be placed together into another bowl, from which one eligible group winner would be drawn and paired with the runner-up.
How the draw farce unfolded...
Draw starts: Benfica are the first team drawn from the runners-up pot - and subsequently paired with Real Madrid.
Villarreal error: Villarreal are drawn from the runners-up pot as Marchetti said: "Villarreal can be paired against all the other seven teams". Arshavin draws Man Utd from the pot of eligible opponents, prompting Marchetti to correct his earlier assertion and say: "This is not possible because Man Utd were in the group so we need to do another one."
Apology: Arshavin instead draws Manchester City but Marchetti apologises for "the technical issue that our draw is experiencing" as a delay occurs in City's name appearing on screen as Villarreal's opponents.
Man Utd missing: Atletico are drawn from the runners-up pot as Marchetti says: "The possibilities are all except Liverpool, who were in the same group, and Manchester United; Manchester United have already been drawn." Manchester United have not already been drawn but Heselschwerdt appears to pick Liverpool and miss picking Man Utd when placing balls representing Atletico's eligible opponents into the bowl. Arshavin draws Bayern to face Atletico.
Draw concludes: The rest of the draw is concluded, with Liverpool drawn against Salzburg and Man Utd eventually drawn against PSG.
Re-draw? The draw concludes but reports emerge of clubs immediately questioning the draw. Sky Sports News contacts UEFA about the possibility of a re-draw.
Draw void! UEFA admits a "technical problem with the software of an external service provider that instructs the officials as to which teams are eligible to play each other" caused a "material error" and declares the draw void, to be re-done later on Monday afternoon.