US Open champion Dominic Thiem admits that he faces a stiff challenge to keep tennis high up in the public consciousness once Roger Federer, Rafael Nadal and Novak Djokovic call it quits. Thiem, 27, captured his maiden Grand Slam title in New York with a breathtaking five-set win over Alexander Zverev earlier this month, the first major final in six years not to feature at least one of the 'Big Three'. However, US broadcaster ESPN said that ratings for that championship match were down 48 per cent. Both Federer and Nadal opted not to play the US Open while Djokovic was disqualified in the last 16. "I think it's normal, because Federer, Djokovic, Nadal, they are like global superstars, and we are not yet," said Thiem after reaching the second round of Roland Garros with a 6-4, 6-3, 6-3 win over Croatia's Marin Cilic, who was celebrating his 32nd birthday on Monday. "I guess we have to build it up like they did. I think there is a chance to do it, but it comes automatically with a lot of success. That's our challenge to do. "But I think that we are not going to have a problem, because for me, like the new generation, or also my generation, they are super-good characters, interesting characters, a lot of star potential there. The only thing we are missing is the huge success. "I guess that there are less viewers or less interest if Roger, Rafa, and Novak are not there much. It's normal, because as I said, they are global superstars, and I hope we are on the way there." Federer, 39, who is sitting out the rest of 2020 to rehab knee surgery, is the record Slam title holder with 20 triumphs, followed by Nadal with 19 and Djokovic, currently the world No 1, with 17. Thiem has finished runner-up to 12-time French Open winner Nadal, 34, at the last two Roland Garros finals. Djokovic, meanwhile, is the 2016 champion. The 33-year-old Serb is bidding to become the first man in the modern era to win all four Slams twice. Thiem is 27 so has time on his side when it comes to further Grand Slam potential. However, he is seeded to meet Nadal in the semi-finals this year with the Spaniard only having lost twice in 95 appearances at the tournament since his title-winning debut in 2005. "For me, Rafa is the huge favourite here," said Thiem. "Obviously there's a lot of different things going on this year with way less crowd, with the tournament going on three or four months later. It's cold conditions. "But with his name and with his past here at the tournament, he's still the huge favourite." Next up for Thiem is American qualifier Jack Sock, a former top 10 player who is now ranked 310. Sock reached the fourth round in Paris in 2015 where he even took a set off Nadal before losing in four sets. "I heard he's pretty good on clay. I heard he played all right a few weeks ago in New York. I think he's being called the new king of clay after Nadal. He loves it here," said Sock, making light of the challenge ahead.