England has about 100 professional clubs, so let's say 2500 players. Assume a similar number for Spain, France, Germany, Italy, Turkey, Russia, Mexico and Argentina, and twice that for Brasil. 25-30,000.
Lets say 500 for smaller nations: Portugal, Scotland, Holland, Denmark, Norway, Sweden, Swizerland, Greece, Poland, Austria, Hungary, Romania, Bulgaria, Ukraine, Czech Rep, Slovakia, a few Balkan countries, USA, Australian, Japan, half a dozen South American countries, a few of the bigger Afrcan countries, etc. Maybe a total of 40 countries and 20,000 players.
So around 50,000 seems reasonable.