This may or may not be a big assumption to make in answering this question, but one might assume you are speaking from an American point of view:
In most countries, including USA, the most popular sports are team games.
There are some Asian countries, who culturally value individual excellence, where certain individual sports are perhaps the most popular. In some Asian countries, for instance, Table Tennis and Badminton are the most popular sports ... but even within these, the popularity of tennis continues to grow.
Tennis is probably growing in popularity with time in many countries because now that it is fully professional, people see it as a means of making a living - and, possibly, a good one.
To return to the original question proper: Among the "individual sports" available, tennis is probably the most popular sport in most countries in the world ... but most countries still prefer one or another team sport to tennis.
USA would have a number of team sports more popular than tennis - especially, in winter.
Compared to other countries, the US is the third largest country in the world.
Compared to other countries it's rank 107, compared to other European countries it's 18.
Libya's healthcare system is relatively good when compared to the other countries.
Most European Countries play tennis.
There are only a couple native animal in Germany compared to other countries. There are only a couple native animal in Germany compared to other countries.
The economy is doing better in the world's developed countries compared to other countries.
Not particularly, compared to other African countries
Ireland does not usually get extremely cold weather, compared to other countries. There are some deaths from the cold, but not very many compared to other countries.
Tennis is definitely the most popular. There are differences between all the racquet sports.
Palapas are most popular in Mexico, they are very common in Mexican beaches, such as in Acapulco. Other countries, where palapas are very popular, are Honduras and other Central American countries
Hurling is been made popular in other countries through the migration of the Irish.
Not many at all
there are more scientists in UK compared to the other countries.
"As many sites (who are trying to sell this merchandise, and thus may have an incentive to stretch the truth) will tell you, tennis gifts, including balls in the form of jewelry and other knick-knacks, are very popular with tennis players."