From the BBC website
25 June 2019
World number two Rafael Nadal says "it doesn't seem right" that he could be seeded behind world number three Roger Federer at Wimbledon. Wimbledon seeding is different from the other Grand Slams in that it does not always follow world rankings and is affected by grass-court performances. It means Federer may be seeded ahead of Nadal, who could be in the same half of the draw as Novak Djokovic.
"It's just Wimbledon that does it," said 12-time French Open winner Nadal. Speaking to Spanish TV station #Vamos, Nadal added: "If everyone did it, I think it would be appropriate or correct. Either way, being second or third seed, I have to play at the best level to aspire to the things I aspire to.
"It is better to be second than third, but if they consider that I have to be third, I will accept." Wimbledon seedings will be announced on Wednesday and Nadal, 33, is likely to be behind defending champion Djokovic and eight-time winner Federer, who won his 10th title at the grass-court tournament in Halle last week.
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From the BBC website
26 June 2019
World number two Rafael Nadal has been seeded third for Wimbledon this year behind top-ranked Novak Djokovic and world number three Roger Federer.
The Spaniard now has a 50-50 chance of being in the same half as Djokovic and thus could meet him in the semi-finals. Had he been second seed, rather than Federer, he could not have met the defending champion before the final.
Last year's finalist and world number eight Kevin Anderson is seeded fourth, and John Isner moves up to ninth after his run to the 2018 semi-finals. Anderson's elevation to fourth seed means Dominic Thiem, Alexander Zverev and Stefanos Tsitsipas all drop down one position in the seedings compared to their world ranking.
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They didn’t override the rankings last year. There’s just a different formula that’s used for Wimbledon which Roger led last year. It’s an explicit formula and everyone would have known Roger would be seeded #1.