The ATP event in Barcelona is donating 20,000 caps to be turned into face masks, helping with Spain's coronavirus efforts.
The nation has been the second-most affected country in Europe.
The caps will be converted by public workers and volunteers. The first 1,000 will go to local hotels in Barcelona which have set up 200 beds to be used as hospitals. Another 2,000 will be sent to the Ifema complex in Madrid, which has now more than 1,000 beds and will be used as a hospital.
The rest of the 20,000 units will be given away in further donations.
The clay-court event was scheduled to be played in three weeks, but there will now be no play until July 13.