Rafael Nadal looked ahead Wednesday to the latest chapter in his unique rivalry with Roger Federer at Wimbledon but regretted that the two heavyweights may never slug it out at the US Open.Nadal and Federer will meet for the 40th time on Friday in the semi-finals at Wimbledon, in what will be the pairs fourth meeting at the All England Club.Federer won the 2006 and 2007 finals before Nadal claimed the 2008 title in a five-set epic.At Roland Garros, the pair have clashed six times while they have met on four occasions at the Australian Open.But when it comes to the seasons final Grand Slam in New York, the two have never managed to face off on the 24,000-capacity Arthur Ashe Stadium, the sports largest arena.Thats despite Federer having five titles at the US Open while Nadal has three.The 32-year-old Spaniard said that as much as he has enjoyed their rivalry at Wimbledon, the New York gap in their head-to-head record was a source of regret.We played a lot of good matches. Here in this tournament, we played two great finals, 2007 and 2008. Have been two emotional matches.Personally, 2008 was a little bit more emotional for me. But I appreciate the fact that I was part of 2007, too.Then we played a lot of matches all around the world. Only in New York, we didnt play. Thats the only bad news, Nadal said.Two-time Wimbledon champion Nadal was written off as a grass court force when he failed to get beyond the fourth round at the tournament between 2012 and 2017.However, he came agonisingly close to the final in 2018 when he lost to Novak Djokovic in a five-hour, 16-minute semi-final.To play against Roger always is a unique situation. Excited to be back on this court against him after 11 years, added Nadal.Always I say the same -- the opportunities to play against each other every time are less, but we are still here. After tomorrow we going to have another chance, said Nadal.