Here are five things to look out for as United hosts QPR this weekend

All eyes on Falcao United could field as many as four (Falcao, Rojo, Shaw and Blind) competitive debutants, but most interest will be on the Colombian goal machine Falcao, who arrived on loan from Monaco on Deadline Day. The 28-year-old – nicked El Tigre (The Tiger) - is obsessed with finding the back of the net – he scored 72 in 87 games for Porto and 70 in 91 games for Atletico – but there are still lingering concerns over his knee after an anterior cruciate ligament injury in January ended his season and ruled him out of the World Cup. The player himself insists he’s as fit and ready to fire. “Physically I feel spectacular. I have been able to play without any kind of trouble whatever,” he said after Colombia’s friendly with Brazil last week. The spells danger for Rangers. Will the bosses stick with the maligned 3-5-2? 3-5-2, 3-4-3, 5-3-2 or whatever else you want to call it, three central defenders with wingbacks has left a lot to be desired for Louis van Gaal and opposite number Harry Redknapp so far this season. The Red Devils’ defence has consistently looked lost with the system while Tottenham ruthlessly exposed QPR’s defensive deficiencies in a 4-0 thumping in August. Redknapp wants to include his three central defenders, veterans Rio Ferdinand and Richard Dunne, as well as talented youngster Steven Caulker, but he might have to bite a bullet and revert to a back four or face a similar mauling. United legend Paul Scholes admits van Gaal’s back three isn’t working, but says it’s up to the players to adapt. After persisting with the system all through pre-season and for the first three games of the Premier League, it seems unlikely LVG will abandon it just yet. Rio returns to Old Trafford The game will be an emotional one for Rio Ferdinand, who returns to Old Trafford as a non-United player for the first time in 12 years. Ferdinand enjoyed huge success at the Red Devils before being signed by QPR in July. The 35-year-old won six Premier League titles and a Champions League during his glittering stint at the club. Despite his advancing years, many believe van Gaal erred in letting him go, with experience severely lacking in the current crop of United defenders. The veteran will get an opportunity to add further credence to those claims when he lines up against his former teammates. Will the new United signings gel? United has the Premier League most valuable squad, English football’s most expensive ever player (Angel Di Maria) and world football’s premier No.9 in Radamel Falcao, but getting the superstars to gel won’t be easy for van Gaal. Will penalty box specialists RVP and Falcao get in each other’s way? Can Blind cope in midfield without defensively-minded teammates? Will Rooney sparkle or struggle in the No.10 role? Will Di Maria be deployed on the wing, in midfield or as a wingback? One game against QPR won’t answer all these quandaries, but the picture should be a little clearer come full time. Van Gaal said the opportunity to sign Falcao was too good to pass up, but United legend Gary Neville has slammed the decision to let Danny Welbeck leave for Arsenal - a direct rival for the top four. “I can’t work it out and I know I worked with Danny Welbeck last week [with England], but it’s odd. I have to admit I thought the Danny Welbeck sale was a strange one, but that’s just me,” he said on Thursday. ‘Of all the prices paid this summer, there are right backs and left-backs galore who have been bought for $25m, $26m, $27m? ‘How have Arsenal got him [Welbeck] for $27m? I can’t work it out. It has helped out a competitor because Arsenal are the team they are fighting for fourth possibly.” Has LVG opted for square pegs for round holes? Falcao and Di Maria’s high profile arrivals succeeded in - at least temporarily - overshadowing United’s perennial concerns in midfield and defence. The attacking weaponry is there, but has van Gaal opted for square pegs to fit the round holes in his team? Blind and Herrera have been signed to bolster the midfield stocks, but there is still no enforcer to break up attacks, like title favourites Chelsea’s and Manchester City have in Nemanja Matic and Fernandinho respectively. The non-Premier League proven Marcos Rojo has landed to effectively replace two central defenders – Ferdinand and Nemanja Vidic. On paper, United resemble a Ferrari with a Fiat engine. They look flashy but whether they’ve got the engine to perform is yet to be seen. Potential United XI v QPR De Gea Rafael Evans Rojo Shaw Blind Herrera Di Maria Rooney Falcao van Persie Originally published as Falcao, Di Maria give LVG a $260m headache