Cristiano Ronaldo returns to a Manchester United desperate for next 'magnificent' No. 7

Wayne Rooney and Zlatan Ibrahimovic are both tearing it up in MLS, with DC United and LA Galaxy respectively, delivering the goals and match-winning performances they once produced at Old Trafford.

And it is difficult for a day to go by without the likes of Paul Scholes or Rio Ferdinand bemoaning the club's current situation under Jose Mourinho's management and talking of what the team is lacking when compared to United's greats.

It is never easy to be reminded of a golden era when the sun has stopped shining, but Cristiano Ronaldo's return to Old Trafford on Tuesday night with Juventus in the Champions League will offer perhaps the starkest jolt to those brought up on United playing, and winning, with a certain style and self-assurance.

Recent allegations that Ronaldo raped a woman in a Las Vegas hotel room in 2009 -- allegations that the 33-year-old denies -- have ensured that there will be no celebratory welcome planned for the player on Tuesday night.

It will be treated as just another game by United, with the club keen to avoid any suggestion of a public show of support for their former player, but only time will tell how Ronaldo is greeted by the Old Trafford supporters when he walks out onto the pitch.

Back in 2013, when he returned to Old Trafford for the first and only time since his £80 million sale to Real Madrid in June 2009, Ronaldo was given a standing ovation and introduced as the "magnificent seven" by United's stadium announcer seconds before kick-off.

Circumstances are different this time, but from a purely football perspective, it is safe to say that United have never recovered from the sale of Ronaldo nine-and-a-half years ago.

Yes, they have won every major honour with the exception of the Champions League since 2009, but there has been a failure on the club's part to fill the superstar void and, if he really was the "magnificent seven," replacing him with a comparable successor has proved to be mission impossible.

When United announced Ronaldo's world-record sale the noises from the club were clear, both publicly and privately, that the £80m would be reinvested in the team.

Cristiano Ronaldo won the Ballon d'Or during his last season as Manchester United's No. 7Getty

Yet with Ronaldo out of the door, and Carlos Tevez following him the same summer with his controversial move to Manchester City, United spent just £19m on reinforcements, with £16m of that spent on Antonio Valencia, the Wigan Athletic winger, as Ronaldo's direct replacement.

Michael Owen, signed as a free agent after his Newcastle contract expired, took on the burden of wearing the No. 7 shirt vacated by Ronaldo -- a number glorified by previous owners like Bryan Robson, Eric Cantona and David Beckham -- and it was the start of a slippery slope for one of the most iconic shirts in the game.

Since Ronaldo vacated the No. 7 shirt at United, five players have taken it on -- Owen, Valencia, Angel Di Maria, Memphis Depay and current incumbent Alexis Sanchez.

Those five players have scored just 56 goals between them for United since the start of the 2009-10 season and, as a result, turned the No. 7 into just another shirt.

United have tried the fading star (Owen), the cheap and dependable (Valencia), the over-priced galactico (Di Maria), the over-hyped rising star (Depay) and the highest-paid player in the Premier League (Sanchez) in an effort to revitalise the shirt, but none of them has worked out.

Valencia has at least been consistent in his time at the club, but he handed the shirt back after 12 months because he didn't enjoy the pressure of wearing it.

Replacing Ronaldo was always likely to be a challenge for any player at United, but since his departure, there has been a vacuum that is still to be filled.

The world's biggest clubs all need a player who defines the way that they play and Ronaldo embodied United's DNA under Sir Alex Ferguson.

They have not had a player like him since and all of his successors have been ill-equipped to replace him.

Owen's injuries had caught up with him, Valencia was too one-dimensional, and Di Maria, Depay and Sanchez have all lacked the mentality that Ronaldo, Beckham, Cantona and Robson had when elevating the status of the No. 7.

Sanchez is less than 12 months into his time at United, so the Chilean may yet come good, but the club's supporters are becoming accustomed to having their hopes dashed.

Ronaldo's return will simply offer another glimpse back to past glories that United are struggling to rediscover.