While further big spending had been predicted in this month’s transfer window, much of the speculation swirling around Manchester United continues to surround a player already at Old Trafford. As well as their lackluster performance, United’s 1-0 defeat to Southampton on Sunday drew much scrutiny for the absence entirely from the team sheet of Radamel Falcao. Having struggled to justify the massive outlay made on him in a season-long from Monaco, the Colombian striker watched on from the stands as United toiled and fresh doubts were raised about whether the club would go through with a permanent deal at the cost of £43 million.

Hampered by injuries and still trying to regain the sharpness lost from a serious knee injury suffered almost exactly a year ago, Falcao has scored just three goals. And the 28-year-old’s agent has conceded that a permanent transfer to Old Trafford at the end of the season is far from a foregone conclusion.

“He is a fantastic player, and I think it's very difficult for Manchester United fans,” Jorge Mendes said, reports Sky Sports. “They have an absolutely brilliant player, one of the very best in the world, who would without any doubt play 90 minutes of the match, every time, with any other club.

“The truth is, right now we don't know what will happen. What we do know is that he will play in one of the very best clubs in the world next season, whether that is Manchester United or not. I am 100 percent sure of that. But you know how football works, we need to wait a little. We'll see what happens.”

Juventus, Real Madrid and Manchester City have previously been linked with a deal for Falcao, but, as things stand, all will surely have doubts about paying the hefty sum it would take to secure his signature. Potentially, that could mean Monaco, who have undergone some serious cost-cutting in recent months, lowering their asking price.

With Javier “Chicharito” Hernández expected to be sold following his loan spell at Real Madrid and Robin van Persie still short of his best and now in the final 18 months of his contract, Manchester United’s forward line could be set for some radical changes in the coming months. It would still be a major surprise, though, were Bayern Munich’s Thomas Muller to become one of the players to occupy the attacking positions at Old Trafford. Still, that is the rumor relayed by the Daily Star this week, with the suggestion that the World Cup winner is eager for a move away from the German champions.

Muller has previously revealed that there was interest from Louis van Gaal in reuniting with a player he did much to develop during his spell in charge of Bayern. However, the 25-year-old stated that there was never any prospect of it happening as he had just signed a new deal tying him to Bayern until 2019. It is difficult to imagine that situation having drastically altered since.

While he may seek to continue to evolve a squad that has won just once in their last five Premier League matches and are only just clinging onto the final Champions League place, Van Gaal faces a tough task to get the players he wants in January. It is perhaps surprising that, according to The Guardian, he still believes that Borussia Dortmund’s Mats Hummels is attainable in this month’s transfer window.

Dortmund find themselves in a shock relegation battle, but that may only increase their resolve not to allow the latest in a long line of key players to depart at this stage. Meanwhile, Hummels has consistently reaffirmed his commitment to the club. Dortmund also offer the attraction of remaining in the Champions League.

Another player long linked with a transfer to Manchester United is Sporting Lisbon midfielder William Carvalho. Interest is in the Portugal international is believed to have cooled after Van Gaal replaced David Moyes in the summer, but Carvalho has certainly hinted that he would welcome an approach.

“My dream is to play in England,” he told Portuguese publication Record, according to the Daily Mirror. “I know some clubs are interested but my agent Jorge [Mendes] is looking after it and I am relaxed. Now my mission is to work in Sporting and they will be in charge of any transfer and my future. That is very important.”