Andy Murray and Alexander Zverev have been awarded wildcards and added to an incredibly strong Rotterdam line-up.
Three time Grand Slam winner Murray is currently outside of the top 100 in the world, meaning he missed out on automatic qualification for the draw.
Zverev, meanwhile, missed the deadline to enter as he was waiting to see how deep he would go at the Australian Open.
There will remain a doubt about Daniil Medvedev and Stefanos Tsitsipas, though, following their fine runs in Melbourne.
"It will be a very strong field now", tournament director Richard Krajicek said.
Asked if he was confident Rafael Nadal would still play, Krajicek said: "He has not gone as far as he could in Australia.
"He is always a positive, driven guy. I think he is already working on Roland Garros. He has also said that he needs matches."
Full entry list for Rotterdam (as of 19/2/2021)
Rafael Nadal (1)
Daniil Medvedev (2)
Stefanos Tsitsipas (3)
Alexander Zverev (WC) (4)
Andrey Rublev (5)
Matteo Berrettini (6)
Gael Monfils (7)
Denis Shapovalov (8)
Roberto Bautista Agut
Alex de Minaur
Jannik Sinner (WC)
Kei Nishikori (WC)
Andy Murray (WC)
The wild cards received by Murray and Zverev are the final two, meaning currently there will be no Dutch players involved in the singles.
However, should anyone withdraw, the wild card currently used by Sinner will pass to Botic van de Zandschulp.
Rotterdam, which was won last year by Gael Monfils, is due to get underway on March 1.
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