From the beginning, the former World number 1 had raised great doubts about his participation in the New York Slam, where he won the final against Daniil Medvedev previous year.
"The health situation is very complicated around the world and COVID-19 outbreaks seem to be out of control".
He added: "This is a decision I never wanted to take but I have chose to follow my heart this time and for the time being I rather not travel".
The matches will be played behind closed doors and NY governor Andrew Cuomo had assured that robust testing will be conducted so that the tournament goes ahead smoothly.
Additionally, the fact that Nadal is the reigning US Open champion but will likely be skipping the tournament gives Thiem even more confidence that he can win his maiden Grand Slam title in NY next month. The US Open 1999 did not host the "FEDAL" pair and two decades later, the world witnessed two massive withdrawals from a Slam event.
In June, the US Open was given the green light to be played without spectators due to the coronavirus pandemic.
It's likely he took into account that the French Open - an event he has won a record 12 times - was rescheduled to take place from september 27-Oct.
"Well, I must be clear, in my first final at Roland Garros, against Rafael Nadal, I had no chance of beating him, we all know what he can do in that tournament", asserted Thiem, before going on to say playing Nadal in that final "is probably the biggest challenge I've ever had in my sports career".
Men's world number one Novak Djokovic is still scheduled to take part in this year's competition where he'll be chasing an 18th grandslam.
NY governor Andrew Cuomo gave his public blessing on June 16 for the flagship U.S. tennis event to go ahead, saying that he was "excited" to host the tournament as part of a relaxation of lockdown measures.
The decision puts on hold Nadal's bid to equal Roger Federer's men's record for Grand Slam titles.
Djokovic is one of the seven Top 10 men's players who appear on the initial main draw entry list for the tournament, which is set to be held without fans from Aug 31 through Sept 13 in the neighbourhood of Flushing, New York.
Williams had suggested that the restrictions on entourages would be a consideration for her participation, as it would likely mean that she would have to spend weeks away from her young daughter.
"Everybody knows how much do I love playing in NY". "We are supposed to stay in a bubble area and can only go to the hotel and back to the courts".
The rescheduled French Open, which Nadal won previous year, is due to start on September 27.