Man Utd centre-backs face crucial test
Think of title-winning teams and you can easily recall the centre-back partnerships involved: Hansen-Lawrenson, Bruce-Pallister, Terry-Carvalho.
The problem for Manchester United is their current centre-half duo - Rio Ferdinand and Nemanja Vidic - are both injured at a time when the Premier League race is reaching its climax.
In their places, manager Sir Alex Ferguson is likely to call on Wes Brown and Chris Smalling against Bolton on Saturday as he did against Marseille on Tuesday. The pair have chalked up only six starts in the same team, with Brown often playing at right-back, and only two at the heart of United's defence.
"Centre-backs are totally about partnerships," says former Liverpool defender and Match of the Day pundit Alan Hansen.
"So when it comes to gelling a couple of guys who have hardly played together - one who is inexperienced and one who hasn't played a lot of games - it's not going to be easy.
"It depends on who is involved, but if you have two guys who are good players and instant hits it still takes you six months to form a solid partnership. And I mean six months minimum and that is playing 40 games.
"You've got to know where your partner is going to go, how he is going to go and whether you go with him. Then there is what line you are going to take, how far back you are going to go, who goes for the ball and who covers. They are all questions that take time to resolve."
During the Champions League victory over Marseille, as well as the defeat by Liverpool two weeks ago, there were worrying signs that the centre-back bond between Brown and Smalling was frail.
And the issue has been exacerbated by hamstring problems picked up by right-backs John O'Shea and Rafael in the European tie.
But although they will be tested by Bolton forwards Kevin Davies, Johan Elmander and Daniel Sturridge this weekend, a home fixture will mean United are likely to dominate possession and chances for Bolton's strikers will be limited.
There may also be reasons to be upbeat from the fact that Vidic's calf injury does not seem to be as serious as Ferdinand's. Past evidence suggests Manchester United are more affected by losing the Serb than the England skipper.
Surprisingly, there is little difference in terms of goals conceded, goals scored or United's win percentage when both Vidic and Ferdinand start compared to when neither is available.
That may be explained by facing inferior opposition but take only Vidic out of the team and the average number of goals conceded per game jumps from 0.69 to 0.91.
Take Ferdinand out of the equation and the jump is from 0.72 goals per game to 0.78.
"Obviously, when you have Ferdinand and Vidic together then they are the best option," says Hansen. "I actually think Ferdinand is the better centre-back but if you are going to lose one you might say that Rio might not be as badly missed because of Vidic's leadership, his last-gasp defending and his ability in the air.
"Manchester United have been vulnerable aerially when Vidic hasn't played and against Bolton they could have Fabio and Patrice Evra, who aren't the tallest players, as full-backs.
"Bolton have got Davies, Elmander and Ivan Klasnic, so manager Owen Coyle will be saying 'every chance you've got get in the box and test them out'."
Smalling, who was playing for non-league Maidstone until 2008, could now appear in the Champions League quarter-finals against Chelsea next month, so the 21-year-old is having to do a certain amount of learning on the job.
Brown, on the other hand, is now 31. Despite a career blighted by injury problems, could his experience not shepherd Smalling through games?
"Smalling needs a Vidic-type figure or a Ferdinand beside him to talk him through how to play the game," Hansen adds. "He looks like a star of the future but centre-back play is not really about the individual. If you've got a regular back four and you've got a kid coming in, he'll be the one who is out of sync.
"I have always thought Brown was a decent player whether he is playing at right-back or centre-back. But Wes hasn't played a lot of matches for a long time and he is not the same kind of figure as Vidic or Ferdinand, so he has to look after himself. He can't go looking after Smalling as well. It's the same if Jonny Evans comes in."
Bolton have been buoyed by the loan signing of Sturridge since he joined them in the January transfer window.
Just as their season looked like it might be beginning to stall the former Chelsea striker scored in each of his first three games and Coyle's side have since gone on to reach the FA Cup semi-finals after beating Birmingham.
The 21-year-old's arrival has given a different emphasis to Bolton's attack, with player touches from the recent victory over Everton and the Trotters' defeat by Chelsea showing the different areas he occupies compared to Elmander.
The problem beforehand was that Davies and Elmander often occupied the same space and, with neither blessed for pace, Bolton could not stretch teams as much as they would have liked.
Sturridge has changed that and now Elmander often comes in off the right, meaning Bolton have several options in which to change their point of attack.
"Manchester United are at home so you would expect them to dominate the match but a combination of height and pace is the more difficult one to play against because on the one hand you have to keep the big men away from the box and then on the other you need to defend deep to negate the pace of Sturridge," Hansen says.
"You want to clear up the pitch so the big guys are away from the box but then you are so susceptible to pace because you are leaving space in behind. It's a difficult one to get right. The good news is that it's so much easier at home. If you're away from home, that's where the problems arise."
With trips to West Ham, Arsenal and Blackburn still to come for Ferguson's side, Bolton may not pose the biggest test for Brown and Smalling, should injury problems to Ferdinand and Vidic mean they keep their places.
But if Coyle's improving team can take some of the chances that were presented to Marseille on Tuesday then it could prove to be another nervy encounter for United.