In a spectacular turn of events last night, Manchester United announced that the club reached an agreement with Juventus for the transfer of Cristiano Ronaldo.According to the BBC, the Red Devils have struck a deal worth around £12.8 million, excluding add-ons. The deal has brought the Portuguese, who has won four more Ballon d'Ors and Champions League titles to his kitty, back to Old Trafford after 12 long years.During his first spell at Manchester United, Cristiano Ronaldo racked up a stellar tally of 118 goals and 69 assists from 292 appearances across competitions. While much of the focus of the footballing world is on Cristiano Ronaldo's homecoming, there have been a few intriguing sub-plots that could transpire in the coming months.On that note, here's a look at the five intriguing sub-plots to Cristiano Ronaldo's Manchester United return.#5 Cristiano Ronaldo to play under former Manchester United teammate SolskjaerCristiano Ronaldo and Ole Gunnar Solskjaer have previously played together.Manchester United's current manager and treble-winner Ole Gunnar Solskjaer has previously shared the Old Trafford pitch with Cristiano Ronaldo for a brief period.Ole Gunnar Solskjaer had entered the twilight of his Manchester United career when the club signed Cristiano Ronaldo in 2003. The Norwegian was one of the senior statesmen in the United squad when Ronaldo made the first big move of his career. The duo played together for four years between 2003 and 2007, winning trophies galore in their short time together.As teammates, Cristiano Ronaldo and Ole Gunnar Solskjaer won the Premier League title, the FA Cup and the Community Shield, among others. The Norwegian has always expressed admiration for his former teammate, and he did so a few hours before Cristiano Ronaldo's transfer announcement as well.Ole Gunnar Solskjær on Ronaldo 🗣“I know where professional... but when you play for Manchester United you don’t go to Manchester City”🔴 #MUFCpic.twitter.com/TlMdeGU4uC— Clara 🔴 (@UTDClara) August 26, 2021In a pre-match conference, Solskjaer said:"Ronaldo is a legend of the club, and the greatest player of all time, if you ask me. I was fortunate to play with him and coach him. He's a tremendous human being. Everyone who has played with him has a soft spot for him."#4 Manchester United's problem of plenty in the forward lineMarcus Rashford (centre) and Mason Greenwood (right)Even before Cristiano Ronaldo's arrival, Manchester United were well stocked in the forward department, especially after Jadon Sancho's arrival and Edinson Cavani's contract extension.Most United fans had set their sights on a holding midfielder to strengthen the squad and challenge for domestic and European glory. However, a club like Manchester United could not pass on a legend like Cristiano Ronaldo, so the board sealed the move in a matter of a few hours.While this move will undoubtedly strengthen the Manchester United squad, some of United's current forwards will have to spend more time on the bench, though.Look who's back 👀Fantastic to see you on the mend, @MarcusRashford! ❤️#MUFC— Manchester United (@ManUtd) August 25, 2021The likes of Daniel James and Jesse Lingard will be afforded very little game time after Ronaldo's arrival.After a flying start to the 2020-21 season, Mason Greenwood might have to vacate his centre-forward position to make way for the Portuguese. Solskjaer might consider playing Greenwood in a wider position, but he will face tough competition from the likes of Marcus Rashford and Jadon Sancho. Paul Pogba has racked up five assists in two Premier League appearances this season from a left midfield role, but Ronaldo's arrival could push him back to a No. 6 role.In the strikers' department, Manchester United will have Edinson Cavani and Anthony Martial as back-ups to Cristiano Ronaldo. The Red Devils will definitely have a problem of plenty in the attacking third, but it's one of the best problems a manager can ask for.