Rafael Nadal will go back to world No 1 on Monday after Roger Federer suffered a shock defeat to Borna Coric in the Halle final.
Federer had needed to defend his title at the grass court tournament in Germany to stay at the top, but he was beaten 7-6, 3-6, 6-2 by Coric.
The 20-time major winner had regained the No 1 spot from Nadal last week after he had triumphed in Stuttgart.
Even though he had not been at his best in the earlier rounds in Halle, given he was on a winning streak of 20 matches, stretching back 12 months, he had been expected to defeat Coric.
But, by failing to triumph in Halle he drops 200 ranking points, which put him down to 8720, 50 behind Nadal.
Nadal, who has not played since winning his 11th French Open earlier in June, has not played any grass court tennis yet this season, but is due to train at Wimbledon this week as he prepares for the third grand slam of the season, which begins on July 2.
Federer is defending champion at Wimbledon and he cannot gain any ranking points at the event, as he has the maximum 2,000 from 2017 to defend.
The only way he will leave Wimbledon as No 1 will be if Nadal fails to match his run to the fourth round last year.
