3 things you need to know about Tuesday's Champions League action

Two teams came into Tuesday's Champions League action in similar situations, albeit under different circumstances. 

Last year's runners up, Borussia Dortmund, have been ravaged by injuries to key players this season, with Ilkay Gundogan, Sven Bender, Mats Hummels, Jakub Blaszczykowski and Neven Subotic all missing significant time. 

As a result, they find themselves 20 points behind Bayern Munich. They're playing for second place in Germany now. 

Manchester United are 15 points off the top in England, but no serious football fan can put them in the class of a team like Dortmund.

Knocked out of cups by Sunderland and Swansea this season, David Moyes has enjoyed a nightmare start to his tenure as Manchester United manager. 

Champions League success is his last chance to salvage this season.

Two clubs with two reasons to go for it all in Europe. How did they do? Differently, to put it bluntly. 

Here's everything you need to know about today's Champions League action...

Dortmund blitz Zenit in St. Petersburg

It took five minutes to realize two things.

1. Zenit St. Petersburg hadn't played a competitive match since Dec. 11 due to the winter break in Russia.
2. Borussia Dortmund can give anyone trouble when their big guns are firing. 

A wonderful run by Marco Reus set up Henrik Mkhitaryan's goal in the fourth minute. 

Less than a minute later Reus made it 2-0 off a sublime passing play. 

Oleg Shatov would get one back for Zenit in the 57th minute, but any ideas of a comeback were extinguished by Robert Lewandowski. 

The future Bayern star scored twice in the second half, helping Dortmund register a 4-2 win on the road and effectively winning the tie in the process. 

For Dortmund, it's almost bittersweet. 

Lewandowski is leaving in the summer and rumours surrounding the futures of players like Reus and Gundogan continue to swirl.

Another run to the final would be one hell of a send-off for this talented group. 

Manchester United fall in Athens 

Another week brings with it another question. Was this the worst Manchester United performance of the season?

Clearly it's a bad sign this question has been asked so frequently this year, but the writing is on the wall. This is an average side at best.

David Moyes and the Red Devils fell 2-0 at Olympiakos on Tuesday. 

Alejandro Dominguez capitalized on a deflection in the 38th minute to give the home side a 1-0 lead.

Moyes made zero halftime adjustments to the consternation of pundits and fans alike. 

It didn't take long for Olympiakos to increase their lead. Joel Campbell, on loan from Arsenal, surely made Arsene Wenger smile with his wonderful strike in the 54th minute. 

And that was that. Manchester United can steal this one at home, but for a team that basically needs to win this tournament in order to return to the Champions League next season this was the strongest of wake up calls.

Former Manchester United captain Roy Keane didn't mince words after the game on ITV. 

"There is a lack of confidence and there are some players who just don't have the quality," Keane said, via the BBC. "We've been brainwashed that the Premier League is the best in the world - nonsense. It's the best brand in the world but they have fallen behind, United more than most. They need six or seven players to rebuild the club."

Drogba and Mourinho in the news

On Wednesday we'll see Didier Drogba take on his old Chelsea mates as a member of Galatasaray in Istanbul.

The timing is interesting considering Jose Mourinho's latest foray into the media crucible.

Mourinho was secretly recorded stating he covets Monaco striker Radamel Falcao. The Special One wasn't finished there. "The problem with Chelsea is I lack a striker," he said, according to the BBC. "I have Eto'o but he is 32 years old, maybe 35, who knows?"

Chelsea were at their best under Mourinho when they had a player like Drogba leading the line. 

The Ivorian star had only kind things to say about his former boss in the lead-up to Wednesday's clash. 

These kind of moments are special, because they are very important, very precious. He was the one who helped me to make my decision to come to play for Chelsea.

He was always fair with me. When I deserved to play, I played. When I didn't, I didn't. That is why I respected him so much.

Respect is one thing, but you can bet Drogba would love nothing more than haunting his former team on Wednesday.