According to Tom Hopkinson of the Sunday Mirror, the 21-year-old is being lined up by some of the most high-profile representatives in the world having opted to break ties with Impact Sports Management.
One of those said to be keen on working with Alli is Jorge Mendes, who looks after Madrid star Cristiano Ronaldo, as well as Mino Raiola, who works with United pair Paul Pogba and Zlatan Ibrahimovic.
"Alli has been told by several agents that they are the only ones who can make moves to United or Real happen if or when he decides to leave Tottenham," Hopkinson wrote. "Spurs are adamant Alli is not for sale and, on the contrary, they are at the very early stages of talks over a new deal."
According to the report, Spurs are ready to double the youngster's salary to around £100,000 per week.
Since bursting on to the scene during the 2015-16 season, Alli has been linked with Los Blancos. In January, Neil Fissler of the Sunday Express said the European champions were ready to go "all out" to sign the England international.
Any interest wouldn't come as a huge shock, as the Spurs starlet is one of the best prospects in the game. Per Squawka Football, Alli has had a wonderful 2017:
Squawka Football @Squawka
Dele Alli has now been directly involved in 21 goals in 26 Premier League games in 2017. 14 goals ⚽️ 7 assists 🅰️ https://t.co/hmD5EMyB5c2017-9-23 21:49:01
There will be no desperation on Madrid's part to sign the midfielder, as they are blessed with so many options in this area of the field. Still, the Spanish capital club has always chased the world's best players, and Alli is well on his way to being in that bracket.
Even so, given how serene his development has been under Spurs boss Mauricio Pochettino, you sense it will be a while before the former MK Dons man is ready to move on.
Marco Asensio to Sign New Deal
According to Moises Llorens of AS, Marco Asensio will become the latest Real Madrid player to sign a new contract with the club.
His piece suggested Asensio will agree terms until 2023 in a contract that will include a release clause of a whopping €500 million (£443 million).
B/R Football @brfootball
Marco Asensio will extend his Real Madrid contract to 2023 this week—with a buyout clause of €500m 🤑 (@English_AS) https://t.co/ft5LKv3tLR2017-9-24 08:17:43
As Llorens noted, Madrid are on a spree of securing the futures of their key players, with Marcelo, Isco, Dani Carvajal, Karim Benzema and Marcos Llorente all penning extensions at the Santiago Bernabeu recently.
The report said Madrid will hold back on officially announcing the new contract until after their meeting with Borussia Dortmund on Tuesday.
The 21-year-old has enjoyed a brilliant beginning to the 2017-18 season, and as noted below, L'Equipe recently named him as the finest young footballer in the world:
B/R Football @brfootball
Marco Asensio has been named the best young player in world football by @lequipe https://t.co/HUUO53ivc72017-9-22 14:48:37
There are still areas of his game that Asensio must refine, though the natural talent he possesses pours out every time he's on the ball. The Spain international is balanced, strong and can do incredible things with his left foot; it's no surprise Real are showing such faith in him with this deal.
The challenge for Asensio is to make the step up from being an incredible prospect to a world-class talent. Madridistas will have little doubt he can do so.