5 tough decisions Louis van Gaal faces ahead of Manchester United's clash against Chelsea

Manchester United boss Louis van GaalSunday, 26th October, sees mentor and protege – Louis van Gaal and Jose Mourinho – go head-to-head in what will be only their second competitive match as rival managers. Old Trafford will play host to league leaders Chelsea, in a match billed to be a tactical battle between two highly successful and versatile managers. The one time the duo faced each other was the Champions League final of 2010, where Mourinho's Inter triumphed over Van Gaal's Bayern 2-0. The Dutchman will be looking to settle scores, but goes into the match with the underdog team. Chelsea's flying start to the league, coupled with Manchester United's stuttering campaign, makes them clear favourites for the tie on Sunday. Although the "underdog" title might not appeal to Van Gaal, a serial winner, it might end up playing into his hands. Jose Mourinho usually likes matches against big teams to be tight, cagey affairs, and the Portuguese usually approaches matches against sides of the ilk of Manchester United with a "must not lose" mentality. But with Chelsea expected to blow away a Manchester United side that looks out of sorts and a work-in-progress, Mourinho might need to take a different approach, lest he be accused of being too cautious against an opponent possessing a porous defense and ponderous strikers.Van Gaal faces difficult questions in the build-up to the match. With no clear playing XI yet, it is possible that Sunday could see a vastly different United side lining up at Old Trafford than the one that took the field against West Brom last week.

#1 Robin van Persie or Radamel Falcao?

Never mind the fact that van Persie has only netted twice this season; it's the fact that he looks uninspiring and/or unfit that should cause concerns to Van Gaal. Any team in the world would want an in-form Van Persie, but the Dutch striker has struggled lately.

And the stuggle is not only limited to his goal contribution. Passes going awry, a distinct lack of understanding with his new team-mates and below par performances have seen van Persie's contribution to Manchester United being of little or no relevance. That is a fall from grace for a player who, up until last season, was seen as the catalyst of all things good.

Falcao, on the other hand, has offered more in his cameo performances than van Persie has in his full 90 minutes. The Colombian looks sharper with each match, and while he has yet to show his full repertoire of tricks, he has certainly shown enough to be starting each week – perhaps at the cost of Van Persie.

It's a difficult decision, but as Jamie Carragher pointed out ahead of Liverpool's Champions League clash against Real Madrid, there can be no passengers in big matches.

#2 Sit deep or press high up?

Mourinho's teams of the past were famous for their ability to counter-attack at breakneck speed. This Chelsea side exhibits the same characteristics.

With the likes of Hazard, Willian, Oscar and Diego Costa being fed accurate balls by Fabregas and Matic, there is enough pace and ability in this team to exploit gaps behind the opposition defense.

The smart money, therefore, would be on Van Gaal opting to instruct his players to sit deeper, and not press the Chelsea players high up the pitch. United's back-four is vulnerable enough; there is no need to load them with further problems.

There is another reason for Van Gaal to ask his team to play with a low block. Last season, Chelsea struggled to break down oppositions that refused to attack them and leave space behind. Although Fabregas' throughballs and Costa's finishing have since been added, there is still a question mark as to whether Chelsea can eke out wins against such tactics.

Control the space, and control the match – that will be Van Gaal's message.

#3 Midfield composition

Although United have been unlucky with injuries up until now, slowly but surely they are getting close to having a full roster for Van Gaal to select from. And against a team like Chelsea, the midfield composition could potentially make or break United.

In the absence of Michael Carrick, Daley Blind has cemented his place in the side as the metronomic midfielder who keeps things ticking over. Ander Herrera, after a fantastic start, is yet to regain full match fitness following an untimely injury. With his constant movements, aggression and ability to bring others into play, Herrera is sure to feature in the match.

Here lies the dilemma – with Mourinho likely to play three of Oscar, Willian, Fabregas and Matic, what does Van Gaal do? Does he try to match Chelsea numerically in the middle, or play with only two central midfielders and add an extra attacker?

Fellaini's return to match fitness is sure to contribute to his final decision. A physical presence is necessary against the likes of Costa and Matic, and so the Belgian could yet be called upon for this game.

A midfield three of Fellaini, Blind and Herrera looks good on paper, and could be enough to blunt Mourinho's marauders. But then that leaves room for only three of Mata, Di Maria, van Persie, Falcao and Januzaj.

#4 Full backs too attack-minded?

The match against West Brom would have given Van Gaal some serious headaches. The two goals that the hosts scored came from a system failure rather than individual errors. While it would be easy to blame Rafael or Shaw for their enthusiasm to attack, it's safe to say that neither did anything that their manager did not ask for.

If the fullbacks are being asked to support the attack at all times, then naturally they will be out of position when the ball is turned over. While West Brom did not take full advantage of United's defensive frailties, Chelsea will not be so forgiving.

With a number of players expected to be returning from injury, it might not be the worst idea to shore up the defense. Rojo and Jones have looked decent, if not excellent, but if one of Smalling, Evans or even McNair is fit to play at CB, then Rojo can be pushed out to left-back – a position that the player excelled in, in the match against QPR.

#5 What are Chelsea\'s weaknesses, if any?

This will be the biggest conundrum facing Van Gaal. Chelsea have so far looked indestructible in all their matches, with no clear weak areas.

A defense that looks solid and communicates well, a midfield that is equal parts physical and creative and an attack that interchanges, and scores, at will – all areas of Chelsea's line-up are well-drilled and invulnerable to scrutiny.

It's up to the Dutchman and his staff to spot any chinks in the armour, a task easier said than done. If ever there was a time to pull a rabbit out the hat, now is that time.

It is Chelsea's match to lose, and United's to show that they are better than what their performances so far indicate, and that Van Gaal's philosophy is slowly shaping the team.