Roger Federer, employing all the verbal dexterity he brings to any discussion on tennis, on Thursday lent his voice to the suggestion that Andy Murray’s reign at No1 in the world is under serious threat for the rest of the summer.

“Andy was tired after getting to No1 at the end of last year and then has been struggling with injuries,” the 35-year-old Swiss said in Halle before his fighting 7-6 (7-4), 6-4 win in an hour and a half over Mischa Zverev, the German left-hander who dumped Murray out of the Australian Open in the fourth round.

Federer, who is returning after taking 11 weeks off the Tour to prepare for his pursuit of an eighth title at Wimbledon, added: “I think the second part of the season will be really crucial for Andy, and Novak [Djokovic] as well. I think the second half of the season is going to be really, really interesting.”

The win puts Federer into the quarter-finals of a tournament he has won eight times, against the world No134, Florian Mayer, but more pertinently lifts him back to No4 in the world, which keeps him away from Murray at Wimbledon until at least the semi-finals.

Federer, Rafael Nadal, Djokovic and Murray have allowed only occasional challenges to their hegemony for more than a decade. Now there is insurrection in the air before Wimbledon: fans have deserted Murray, the defending champion, to back Federer into 5-2 favouritism, according to Ladbrokes. If he wins a ninth title in Halle, he will edge up to No3 seed at Wimbledon.

At Queen’s Club this week, the vulnerability of Murray and Stan Wawrinka, who refuses comparison with the supposed big four despite reaching his fourth slam final at Roland Garros this month, was painful, for them and their supporters.

Murray, the five-time champion, lost to Jordan Thompson, a young Australian hustler ranked 90th in the world, while Wawrinka went out in two sets to Feliciano López. Neither of them was as poor as Djokovic at Roland Garros but they were plainly frustrated in their preparation for Wimbledon.

Djokovic, who plays Eastbourne next week, a rare warm-up on grass before the championships at the All England Club, is probably in deeper trouble after his meltdown in Paris against Dominic Thiem, while Nadal, who beat Wawrinka there for his Decima, withdrew from this tournament to safeguard his knees.

Uncertainty has gripped the game again, which will lend Wimbledon added edge when the first ball is struck on 3 July. So, when the man who beat the man, Thompson, lost here on Thursday to the other man who beat the other man, Sam Querrey (Djokovic’s conqueror at Wimbledon last year), a degree of normality was restored to the tennis landscape.

The American, 62 places clear of the Australian lucky loser at 28 in the world, was three points away from the quarter-finals when Thompson smashed his way back into the fight to hold for a 5-3 deficit. But Querrey’s serve was too solid in the ninth game, and a 15th ace helped secure the win. He next plays Gilles Müller, who put out the No5 seed, Jo-Wilfried Tsonga, in the second round.

The tournament has been so fundamentally shredded with the departure of the top two seeds, Murray and Wawrinka, not to mention Tsonga, Milos Raonic (No3) and Nick Kyrgios (No9), that nobody is safe from this point onwards. When the 2012 winner Marin Cilic goes against the American left-hander Donald Young in the quarters, having blitzed Young’s teenage compatriot Stefan Kozlov in 56 minutes on Thursday, he may be the first bankable favourite of the week.

The Croat allowed John Isner only eight games in the first round and Kozlov – who had never faced a top-10 opponent – only four. On form and history, he deserves to be the bookmakers’ choice to succeed Murray as champion on Sunday.

Cilic said of the top-flight wreckage this week: “It happens quite often, especially as we are playing so many tournaments during the year. It’s very rarely that all the top seeds are going through. It’s not easy, especially at a tournament like this where there’s so many great grass-court players.”

Müller, playing some of his best tennis in a while at 34, may have too much firepower in his lethal serve for Querrey, but probably not enough quality movement to beat Cilic in the semi-final.

On the other side of the draw, the No6 seed, Grigor Dimitrov, who took three tough sets to see off Julien Benneteau in the second round, plays the Russian Daniil Medvedev, who beat the returning Australian Thanasi Kokkinakis in under an hour, 6-2, 6-2.

In the remaining quarter-final, the No7 seed, Tomas Berdych, plays López, who won 6-1, 7-6 (7-4) against the Frenchman Jérémy Chardy.

Konta crashes out as Coco seals sweet win

Johanna Konta lost 6-1, 6-3 to Coco Vandeweghe in Birmingham but says she is happy with her recent form. Photograph: Mike Egerton/PA

Johanna Konta believes her Wimbledon preparations are still on track despite a disappointing Aegon Classic second-round defeat to Coco Vandeweghe.

The world No7 crashed out in Birmingham after a 6-1, 6-3 loss to the American, a grass-court specialist who reached the fourth round at Wimbledon last year. Konta was beaten in the final of the Aegon Open last week by Donna Vekic as she failed to take the opportunity to win a first title on home soil. Konta does not believe the early exit in Birmingham is a blow to her buildup to Wimbledon and said: “Me losing in the second round against a very good player on this surface is by no means a blow. It’s part of the game.

“Just because I am No7 in the world does not mean I am entitled to winning every single match. I think I actually played two good matches here. I played a very good first round against someone who made the semis last week in ‘S-Hertogenbosch – I think I played a great match there. Last week I played five great matches. I lost to a player who played better than me.

“For the moment it’s very uncomfortable, and there is a question, I think, about it, because the season is still long and there is lots of big tournaments as well where I will feel more comfortable on the hard court.” PA