Manchester United have been linked with transfers to bring both Cristiano Ronaldo and Gerard Piqué back to Old Trafford. Since the arrival of Louis van Gaal as manager, the English giants have shown a willingness to spend big in order to bring the club back to the top in England and Europe after a disastrous single season under David Moyes in which they finished seventh in the Premier League. According to reports, that outlay could continue in order to secure Ronaldo and Piqué from Spanish giants Real Madrid and Barcelona, respectively.

Talk of Ronaldo moving back to the club he left for a then record £80 million transfer fee in 2009 is nothing new. There was strong speculation that United were actively pursuing the possibility of re-signing the Portuguese star last summer before he signed a new five-year deal at the Bernabeu to make him the then world’s highest-paid player. But speculation of Ronaldo’s unhappiness has resurfaced after he voiced his disagreement with Real Madrid’s decision to sell Angel di Maria -- to Manchester United -- and Xabi Alonso this summer. As well as the Ballon d’Or winner continuing to express his love for the club with which he played for six years, Van Gaal did not rule out the possibility of Ronaldo returning when speaking last week.

“Yes, but it's always a discussion in the papers, and I don't think the media shall buy Ronaldo,” he said, reports Sky Sports. “It is possible. That's what I have said with Falcao. Players like Ronaldo give a lot of extra to a team, but I don't think Real Madrid shall sell him.”

Speaking after he scored four goals against Elche on Tuesday, though, Ronaldo reiterated that he had no plans to leave Madrid any time soon. “They are all speculations about my future, he said, according to the Daily Mail. “My future is Madrid. I'm happy this season is going well, and my future, I will not speak about, it does not make sense.”

That a section of Manchester United fans are paying to fly a plane displaying a banner with the message “Come Home Ronaldo” over Villarreal’s stadium when Ronaldo and Madrid play there on Saturday, shows how fondly he is still regarded by supporters. Yet, anyone that has watched United’s early performances this season, particularly a 5-3 defeat to Leicester City on Sunday, will be in no doubt that the priority in further strengthening the squad lies in defense.

And Spanish publication AS believes United are keen to remedy their issues at the back by bringing Piqué back to Manchester in January. Having been snapped up from Barcelona’s youth ranks as a 17-year-old, Piqué spent four years at Old Trafford without becoming a first-team regular before he was allowed to return to the Catalans for just £5 million in 2008. But the Spain international has seen his place come under threat this season from the arrival of Jérémy Mathieu, prompting talk that he would be interested in rejoining Manchester United. A major potential stumbling block to the deal, however, is a transfer ban that prevents Barcelona from signing players until January 2016. Such a restriction will surely make Barcelona reluctant to ley any experienced players leave.

There remain rumors that Van Gaal will instead turn to a man who served him well during the 2014 World Cup, Dutch center-back Ron Vlaar. The 29-year-old will be out of contract at Aston Villa next summer, further prompting speculation that he could be on the move. However, the Daily Mirror has reported that Vlaar is now prepared to sit down and discuss the possibility of a new deal, although he is still keeping his options open. While hardly a signing to wow United fans, Vlaar would offer some solidity to a currently struggling back line.

As well as a center-back, Manchester United also arguably failed to address the need for a commanding central midfielder over the summer. After months of incessant speculation linking him with a transfer to Old Trafford, Arturo Vidal remained a Juventus player at the end of the window. It was believed that United were hesitant to pay the hefty fee it would take to prize the Chilean away from the Italian champions because of a knee operation he was forced to undergo at the end of last season.

But, according to the Daily Star, United are considering making a bid of £35 million in January. After a thigh injury added to his fitness troubles at the start of the season, Vidal returned in style with two goals against Cesena on Wednesday. His progress will likely continue to be followed closely by those at Old Trafford ahead of the reopening of the transfer window.