For at least the past 18 months, Novak Djokovic has been the dominant world No. 1 and a prohibitive favorite going into each of tennis’ Grand Slam events. In that context, the 2016 U.S. Open looks positively wide open. Not only are there concerns about multiple injuries affecting Djokovic, but Andy Murray is enjoying a glory-laden summer while Rafael Nadal is back in the mix.

Djokovic may still be the safe bet in the eyes of many to take home the trophy a week on Sunday, but that money no longer looks as secure as it would have done not long ago. After claiming victory at the four previous Grand Slams, including last year in New York, Djokovic suffered a shock early exit at Wimbledon. And his summer has not gotten much better since.

He lost in the first round of the Olympics while hampered with a left wrist injury that also forced his withdrawal from the Cincinnati Masters 1000 event. With talk about his wrist dominating the buildup to the U.S. Open, Djokovic then received treatment on his right arm during his opening match in New York against Jerzy Janowicz. After the four-set win, which saw him lose a set in his opening round of a Grand Slam for the first time in six years, Djokovic failed to put the injury concerns to bed, stating that he was taking it “day by day.”

He will have been grateful then to get an extra two days to rest his ailments thanks to Jiri Vesely withdrawing from their second round match with an injury of his own.

Meanwhile, the man who is now suddenly a threat to his No. 1 ranking has breezed through the opening two rounds in straight sets. Murray is certainly the player in form, having won the title at both Wimbledon and the Olympics, while also reaching the final in Cincinnati despite arriving with no rest after his exploits in Rio de Janeiro.

With Ivan Lendl back in his corner, Murray is playing confidently, aggressively and with a steely focus on adding to his three Grand Slam titles and getting to the top of the rankings for the very first time.

It would appear a two-way battle for the title at Flushing Meadows, particularly with the player who Murray beat in the final of Wimbledon, Milos Raonic, bowing out in the second round after suffering debilitating cramps.

But Nadal, who has been afflicted by a string of ailments in the past two years, could yet have something to say about the outcome of the final major of the 2016 tennis season.

Nadal was forced to withdraw from the French Open and then sit out Wimbledon because of a wrist problem, but has shown immediate signs of a return to the encouraging form he displayed before his latest injury. The 14-time Grand Slam winner has lost just 13 games on his way through to the third round and, helped by Raonic’s withdrawal, a relatively kind draw through to the semifinals.

Were he to get that far, Nadal could face Djokovic, who he beat to claim his two Grand Slam titles in 2013 and 2011. Whether that tantalizing match transpires or not, the men’s draw at the U.S. Open is far more intriguing than anyone had a right to expect at the start of the tennis summer.