Manchester United will be heading into this game with an air of caution as 0-0 is a very delicate scoreline.
You've not got an away goal as a safeguard and when you're the home team you can suffer from over confidence and believe that the job is already done. And then one good moment from the opposition and you're chasing the game.
So Sir Alex Ferguson will be making sure his side are completely switched on because Marseille are certainly capable of giving United a scare. They are not the best team left in the competition but they are full of physical and athletic players. And they're not bad travellers, either.
I remember they beat Liverpool 1-0 at Anfield in the 2007/08 group stage and they have also claimed some good victories away from home in this year's competition; 3-0 at Spartak Moscow and a 7-0 thumping of MSK Zilina.
Those clubs aren't up to United's level but it proves that Marseille know what it takes to play - and win - on the road. United's unbeaten home record this season is under legitimate threat.
With Rio Ferdiand still missing, Chris Smalling looks likely to partner Nemanja Vidic in central defence. He has proved a capable stand-in but Marseille probably will be targeting him.
They are a big side with the likes of Souleymane Diawara and Stephane Mbia at the back, while Gabriel Heinze is also very good in the air, and United are a pretty small team in comparison. You'd think that overpowering their hosts will be one of Marseille's main plans.
However, Didier Deschamps will be delighted to have playmaker Mathieu Valbuena - who came on as a late substitute in the first leg - back to full fitness and if he gets time on the ball, he could create some problems for United.
He scored the goal when Marseille beat Liverpool, but he has come on leaps and bounds since then and has blossomed into a top player. They rely on him for direction from the middle of the park and he could provide the spark that Marseille lacked at the Stade Velodrome.
It will be interesting to see if Paul Scholes starts; he and Valbuena are alike in stature, they play similar creative roles and both have a goal in them - they could have a really intriguing battle. Scholes is suspended for the next two league games, so I do suspect he will play from the off.
It was great to see Antonio Valencia return from that horrific ankle break against Arsenal at the weekend and he got a 45-minute run out that will do him the world of good. I think Sir Alex will want to wrap him up in cotton wool, so I don't see him starting. But if it's 0-0 going into the second half and United need an injection of pace and guile, he could be that man.
Nani has also been declared fit and I'd be surprised if he didn't start, because no-one gives United width like him. He's got that nasty gash on his leg and that will need monitoring and probably a lot of protection, but he is a match-winner and Marseille won't want to line up against him.
But whatever side Sir Alex selects should be good enough to secure United a place in the quarter-finals.
THOMMO'S VERDICT: I think United will go through, even though it could be tricky. I don't envisage Marseille going for goals from the kick-off; they'll probably play 4-5-1, try to stifle United and then hope to score through a set-piece. United, though, have become experts at doing enough in Europe and they should win the game by the odd goal. I'll say 1-0 or 2-1, and United to maintain their record of never having lost at home to a French side.