Ole Gunnar Solskjaer was sacked as Manchester United manager on Sunday after nearly three years in charge - and Paul Merson believes that the return of Cristiano Ronaldo to the club over the summer is partially to blame. 

Five-time Ballon d'Or winner Ronaldo arrived from Juventus for a second stint at Old Trafford in late August, some 12 years after he had initially departed the Theatre of Dreams for Real Madrid. 

While United fans celebrated the signing of the 36-year-old as a monumental moment for the club, the fact remains that it was very much a last-minute deal - to the point that Ronaldo didn't officially become a United player again until transfer deadline day. 

With the new Premier League season already several games old by that point, Solskjaer already had his plans in place for the new campaign. United had splashed out £73 million on Borussia Dortmund winger Jadon Sancho - and also handed a one-year contract extension to veteran striker Edinson Cavani.

Both players would be heavily impacted by the shock return of Ronaldo.

Writing in his column for Sky Sports, Merson suggested that Sancho and Cavani had been earmarked as key men by Solskjaer for the current campaign, before the sudden presence of Ronaldo caused all previous plans to be drastically altered.

"I feel sorry for Ole Gunnar Solskjaer," admitted Merson. "He had a plan at the start of the season, having finished second last season. He's chased Jadon Sancho for a long time, got him in, and he's given Edinson Cavani another year. 

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Merson: "United aren't a better team with Ronaldo in it"

"Then, he gets given Ronaldo. I think he's thrown it all out of the window. From day one, they're not a better team with Ronaldo in it.

"You don't go 29 games unbeaten away without playing a certain way, and bringing Sancho in gave them another weapon to play that way.

"With Ronaldo up there, you don't have that weapon to play on the counter-attack anymore. And Bruno Fernandes was their best player last season - he's hardly had a touch this season!

Solskjaer, Fred and Fernandes following Man Utd's 4-1 defeat to Watford

"It's all snowballed for Solskjaer. He had a plan, and the Ronaldo situation threw it all out of the window, just before the season started."

Merson even claimed that United would not have been tempted to bring Ronaldo back to Old Trafford had it not been for rumours regarding a possible move for the Portuguese superstar to fierce rivals Manchester City.

"They only went for him because they heard Man City were after him. It's not like United were calling Juventus to ask if he's available because Ronaldo is the missing link for United winning the Premier League. He isn't!"

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Since his return to English football, Ronaldo has found the net nine times in 13 appearances for the Red Devils.

Five of those goals, however, have come in the Champions League in which - without Ronaldo's intervention - United would already have been eliminated.

Despite Ronaldo's herculean effort in Europe's premier club competition, Merson feels that the benefits of having the star in the fold are outweighed by his overall negative effect on United's shape and style of play.

Solskjaer was shown the door by United on Sunday

The former Arsenal playmaker also argued that Solskjaer found himself in a situation where he couldn't drop a figure with as much influence as Ronaldo.

"Solskjaer tried to drop him against Everton in early October - people say he rested him, but they had internationals the week after! He was hoping they'd beat Everton to justify him keeping the same team. That backfired, and all of a sudden, he had to go back to playing him every week.

"They chased Sancho for 18 months, they get him and he doesn't play a game. People are saying they didn't need Sancho, but he was perfect for the way they played counter-attacking football. Now they can't counter-attack, and the plan completely and utterly went out of the window.

"It's not Ole's fault, he didn't buy him!"

"It's a problem going forward. The fans love Ronaldo, he's the king. Don't get me wrong, he's been one of the best players in the world, but this is the Achilles heel. The bloke is a legend, with the records he's put up, but that's not today.

"He's a legend. I'm not having a go at Ronaldo, and he'll go down as one the best to ever play football.

"But I got shot down from day one on transfer deadline day. I got slaughtered for saying they were further away from winning the league the moment they signed him than they were before. It's not Solskjaer's fault - Solskjaer didn't buy him," declared Merson.

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Both Ronaldo and Solskjaer are legendary figures at Old Trafford. However, football is a results business - and the recently axed United boss simply didn't pick up enough points in the Premier League for him to retain his role.

Whether or not things might have been different had Solskjaer not had to hastily rearrange his plans to accommodate Ronaldo is a question that will never be answered.

Whoever becomes United's next permanent manager, though, will face a similar conundrum as the Red Devils battle to save their season.