All have been supposedly monitoring Chelsea goalkeeper Thibault Courtois very, very closely. The Belgian is the Blues' undisputed No.1 but in a little over a year's time will be free to discuss a move to any of the aforementioned sides ahead of his contract expiring in the summer of 2019.
The Blues, , had planed to make Courtois the best-paid goalkeeper in the world to keep him at Stamford Bridge and a deal is close to being inked.
Courtois will reportedly earn, including bonuses, more than the £200,000-a-week David De Gea is paid by Manchester United. More than enough reason to sign a deal that would run to 2023.
The Blues' first-choice stopper was asked in November about his future. While he is understood to be happy at Stamford Bridge, his answer to the question wasn't entirely convincing.
He said: “Regarding my contract, that's the thing where Chelsea must deal with my agent. I don't think there have been any new developments.
“We have so many games at the moment, and I prefer to focus on the team's games, my own performances, and there will be time enough towards the end of the season to have talks.”
This new development would go against what the Belgian was saying and talks would have to take place while the season is still going ahead.
Holding talks at the end of the season is never something Chelsea should entertain. They need Courtois to commit to the club far earlier, otherwise they face being held to ransom next summer with only a year left on his deal.
It's somewhat surprising, and slightly concerning, that it's got to this stage at all. In recent years the Blues have been good at ensuring their star players are all secured on long-term contracts.
Eden Hazard's current deal doesn't expire until 2020 and talks about an extension are ongoing. N'Golo Kanté signed a five-year contract when he joined the club in the summer of 2016. And the terms Álvaro Morata agreed when he joined from Real Madrid tie him to Chelsea until 2022.
So why is Courtois different? Well his relationship with the club hasn't always been the smoothest.
There was a supposed breakdown in his relationship with former goalkeeper coach Christophe Lollichon, who was eventually replaced by Gianluca Spinelli when Antonio Conte arrived at the club.
He has often discussed moving back to Spain, saying in 2016: “From the first minute I loved Spain for its people, the way of life, the food. Today I still have the food and eat dinner late, the siesta, the television I watch most is Spanish. I feel half Spanish.
“The three seasons at Atlético made me the goalkeeper I am now. When I said goodbye I felt bad, it's not easy to make me cry.
And last summer Courtois publicly spoke out about his disappointment with Diego Costa's sale to Atlético. He also reportedly turned down a contract offer from the Blues.
But, ultimately, the only reason Courtois hasn't yet committed his long-term future to Chelsea is the obvious one; money. The Belgium No.1 is currently earning around £100,00-a-week on a contract he signed in September 2014.
Courtois managed to oust Blues legend Petr Čech from the Chelsea goal that season and was rewarded for it. Three years on the reigning Premier League champions must again show their goalkeeper the same respect.
De Gea is arguably the best goalkeeper in world football and the stats this season suggest Chelsea's stopper isn't at the same level.
The Spaniard is averaging a quite astonishing 4.16 saves per goal in the Premier League this season and is conceding just 0.79 per match. By comparison, Courtois stands at 2.05 and 0.79. Meanwhile, Courtois' distribution accuracy is far better than the Spaniard's (76 per cent to 61).
So is Courtios demanding too much from Chelsea? Not exactly. While he may not be at the same level as de Gea, he is two years younger than the United goalkeeper and has, statistically, been better than any of the other ‘big six' No.1s this season.
Manchester City goalkeeper Ederson has been lauded for his performances this term and yet his saves per goal ratio stands at 2.05. Tottenham's Hugo Lloris is making 2.39 stops per goal conceded while Čech (1.48) is well behind.
To paraphrase an old saying, a good goalkeeper is hard to find. The Blues certainly have one and they should pay him accordingly. Fail to do so and they could find themselves in trouble next summer.
Courtois would hold all the chips and that is a dangerous game for Chelsea to be playing.