Latest scores:
Juventus 0-1 Deportivo (agg 0-2)
Man Utd 1-0 Porto (agg 2-2)
Lyon 1-0 Real Sociedad (agg 2-0)
Chelsea 0-0 VfB Stuttgart (agg 1-0)
Goalflashes and major incidents (all times GMT):
2017: Goal. Man Utd 1-1 Porto (agg 2-3)
High drama at Old Trafford as Porto grab a leveller - which puts them ahead on aggregate.
2131: Jesper Gronkjaer hits the post for Chelsea.
2130: Chelsea's Adrian Mutu has two efforts saved within a minute as the Blues try to finish off Stuttgart. It is a tense, tight game at Stamford Bridge.
2118: Sir Alex Ferguson shows his intent by sending on Ole Gunnar Solksjaer as a substitute - United are desperate to clinch this tie.
2017: Goal. Lyon 1-0 Real Sociedad (agg 2-0)
Pernambucano Juninho all but guarantees Lyon a place in the quarter-finals for the first time in the French club's history.
2118: Cristiano Ronaldo replaces Darren Fletcher for Man Utd, who are pressing for the second goal which could kill off the game. In west London, Jesper Gronkjaer fires a shot just over from 20 yards.
2109: Stephen Appiah hits the bar for Juve from 30 yards - but it looks increasingly like the Italian giants are on their way out of the competition. However, there is a delay in this game after the pitchside sprinklers go off by mistake!
2104: Paul Scholes is booked - now he will miss the first leg of the quarter-finals should United progress.
2033: Man Utd's Louis Saha is on for the second half with Eric Djemba-Djemba off injured.
2033: Half-time in the games involving Man Utd and Chelsea - the Londoners are looking slightly more anxious while the Red Devils will be furious at the Scholes effort which was not given.
2032: Paul Scholes puts the ball in the net for what should have been his second of the night but the 'goal' is controversially disallowed - even though the England man is clearly onside.
2017: Goal. Man Utd 1-0 Porto (agg 2-2)
Paul Scholes puts Man Utd level on aggregate, and ahead on the away goals rule, with a trademark nearpost header after excellent work from John O'Shea.
2014: Chelsea defender Glen Johnson is forced to go off with an ankle injury - Marcel Desailly replaces him. The Blues are defending their aggregate lead comfortably so far.
1957: Goal. Juventus 0-1 Deportivo (agg 0-2)
Juve go 1-0 down on the night and 2-0 behind overall as Walter Pandiani tees himself up after a long ball forward and crashes the ball home.
1950: A blow for Juventus, who are trying to overturn a 1-0 deficit, as Alessandro Del Piero goes off with a calf injury.
1945: Wednesday's four matches get under way.
Team news:
Manchester United defender Mikael Silvestre is not fit enough to return. Eric Djemba-Djemba is drafted into midfield in place of the suspended Roy Keane, while Darren Fletcher retains his place.
Louis Saha starts on the bench, as Paul Scholes plays in the hole behind Ruud van Nistelrooy.
Chelsea welcome back Damien Duff, who makes his first start in 2004. Jimmy Floyd Hasselbaink misses out as Hernan Crespo plays up front on his own.