(CNN) -- The battle for men's tennis supremacy in 2012 will boil down to the U.S. Open at Flushing Meadows, according to former world number one Jim Courier.
The American Davis Cup captain has watched the world's top players at close quarters this year and believes there is nothing to divide Australian Open champion Novak Djokovic, Wimbledon winner Roger Federer and Olympic gold medalist Andy Murray.
Rafael Nadal would also come into that category, but the French Open champion will miss the New York event with a knee injury which also prevented him taking part at London 2012.
"The winner of the final slam of the season will have added a second major title to their record and can justifiably claim to be No.1," Courier told CNN's Open Court ahead of Monday's opening matches at the two-week hard-court tournament.
The four-time grand slam champion said Murray's Olympic triumph in the men's singles this month, when where he beat Federer in straight sets in the final, had elevated him to the same status as the other three.
"It used to be three and a half, now it's the big four," Courier said.
"Murray has momentum with him and has been unbelievably consistent."
But when pressed to predict the winner in New York, Courier opted for defending champion Djokovic, believing he can return to the form which saw him totally dominate in 2011 "and on his best surface."
The Serbian started his North American hard court swing by easily retaining his Toronto Masters crown where he beat Richard Gasquet in straight sets in the final.
He can't reclaim the No. 1 ranking from Federer even if he wins the September 8 final, but it would set him up for the end-of-year honors ahead of November's ATP World Tour Finals.
World No. 4 Murray won his opening match in Canada but then withdrew with a knee injury, and suffered a shock early exit in Cincinnati as he failed to defend his title.
With Federer also in superb form, thrashing Djokovic in the Cincinnati final, Courier cannot see outside the top three seeds.
But he nominated 2009 champion Juan Martin Del Potro, who took Olympic bronze at Wimbledon, French world No. 6 Jo-Wilfried Tsonga and John Isner, who has performed heroics in the U.S. march to the semifinals of the Davis Cup, as dangerous outsiders.
"You would not have any of those in your part of the draw," he said.
For Courier, who won two Australian Opens and two French Open crowns, the choice of women's champion is easier.
"Serena Williams," said the 42-year-old, who lost in the finals of the 1991 U.S Open and Wimbledon two years later.
"She played ridiculously well in the Olympics."
Wimbledon champion Williams will be bidding for her fourth U.S. Open crown and 15th grand slam title, but she surprisingly lost to Australian Samantha Stosur in last year's final when looking similarly invincible. She also slipped up in the WTA event in Cincinnati this month with a quarterfinal loss to Angelique Kerber -- her first defeat since exiting early at the French Open in June.
After the U.S. Open, Courier will take the U.S. team to Gijon to face Davis Cup champions Spain as the Americans bid to reach the final for the first time since 2007. They thrashed Federer's Switzerland team 5-0 in February and beat Tsonga's France 3-2 in April.
"We're not going to beat the Spaniards -- but we weren't going to beat the Swiss or the French either," Courier said.
"You look on paper at our matches this year -- away, on clay, against great teams -- we should be playing a relegation match now rather than the semifinals.
"The Bryan brothers, they've won everything, done everything. Isner's been a real threat to everyone he's played in Davis Cup and Mardy Fish came up big for us in Switzerland with a singles win and doubles win. We've put together a true team effort."
Courier will be taking on some of the finest tennis players in modern history in the 12-city Powershare Champions Series that he helped create.
John McEnroe, Andre Agassi, Jimmy Connors and Michael Chang will be among the big names taking part in a whistlestop tour of the U.S. from mid October to the end of November.