Local health authorities have recommended that the Madrid Open, a key warm-up event for the French Open, should be cancelled due to a spike in Spanish COVID-19 cases.
Organisers say that a final decision is yet to be made, stressing that the fate of this year's competition fell into the hands of the tournament's license-holder, Ion Tiriac and Super Slam Limited.
The Madrid Open is due to take place from September 12 to 20, featuring both Association of Tennis Professionals Tour and Women's Tennis Association (WTA) Tour competitions.
The French Open, one of tennis' four Grand Slams, is currently scheduled to take place from September 27 to October 11, having already been postponed this year.
Antonio Zapatero, Deputy Secretary of Public Health in Madrid, has been working closely with the organisers, alongside the National Sports Council.
In their last meeting, on July 29, the recommendation was made to not go ahead with the tournament.
A Madrid Open statement read that "due to the increase in cases of COVID-19 in Madrid in recent days, the organisers of the Mutua Madrid Open stated their concerns about being able to stage the tournament free from health complications that might affect the players, fans and staff.
"In view of this situation, the organisers of the Mutua Madrid Open requested the help of Antonio Zapatero, Deputy Secretary of Public Health, and were advised not to stage the tournament due to the current trend of COVID-19 cases.
"As they have throughout the entire process, in that meeting, the organisers of the Mutua Madrid Open benefitted from the cooperation and help of the Community of Madrid in analysing the situation, which is unfortunately deteriorating day by day.
"As it is impossible to guarantee a positive change in this situation in the coming weeks, the organisers of the Mutua Madrid Open wanted to make a decision in good time."
Spain has seen a steady increase in coronavirus cases since early July, with more than 3,000 reported on the last day of the month.
That figure was only 300 a month earlier.
The statement finished by saying that organisers were "analysing and closely evaluating all the possible options, while always focusing on guaranteeing the safety of all those involved in the tournament".
Tennis' return from the coronavirus-enforced break has not all gone to plan, with an unnamed player testing positive for COVID-19 yesterday at the Palermo Open.
Women's world number one Ashleigh Barty has pulled out of the US Open - due to begin later this month - and fellow Australian Nick Kyrgios has taken the same stance.