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The 22-time grand slam champion has been struggling with a left hip issue that contributed to his second round exit at the Australian Open in January.
Nadal pulled out of hard-court contests at the Indian Wells Open and Miami Open as he continued to recover from the problem.
He could return on clay, his favoured surface, with Massey optimistic the 36-year-old will be fit in time to feature at the event, which begins on April 8.
"Rafa was the first [player] to be registered," he said in statement. "He really wants to play at the Monte Carlo Masters.
"He is giving himself every chance to take part in the tournament he's so fond of."
Nadal is the event's all-time record title holder, having triumphed on 11 occasions, with an Open Era record streak of eight consecutive successes between 2005 and 2012.
He last succeeded in 2018, with a straight-sets victory over Kei Nishikori, though various disrupted campaigns have prevented him from mounting another successful bid since.
As a key stop in preparations for the French Open, it has helped form the bedrock of his clay court success over the years.
With this year's event at Roland Garros set to start on May 28, Nadal will be out to add to his 14 singles titles there too, having claimed victory once again in 2022 with a triumph against Casper Ruud in the final.