"My opinion is that our league has too many clubs," Rosell said during a debate at the International Football Arena conference.
"We have 20 and we should go down to 18, then to 16. This will mean that all the clubs will be more competitive and we can reduce players' salaries."
Describing Spanish football as facing huge financial problems, Rosell added that he was opposed to foreign ownership of the country's clubs and warned that some clubs could disappear.
Rosell said Spain would have to change the system of distributing television money under which the lion's share goes to Barcelona and Real Madrid, putting them at an advantage over their rivals.
"It is the only league where TV rights are negotiated individually and some time in the next three or four or five years we have to put it all in one pot and make the distribution the way it is in Serie A and the Premier League," he said.
"This is something Barcelona and Real Madrid are talking to the other clubs about; we have to listen to the demands of the other 18 clubs."
He added: "The Spanish league is the second most popular [in Europe], but we are facing huge problems financially speaking.
"None of the clubs in Spain are in a good position; we owe a lot of money to the banks.
"[At] Barcelona, Real Madrid, Athletic Bilbao, Osasuna, the situation is not good but it is under control.
"As for the other 16 teams, some are in a very bad position and I don't think they will come back; maybe next year they will go to the second or third division or disappear."
Rosell added: "The most important thing is to reduce the number of clubs for the future and put financial conditions that have to be accomplished, also in terms of people from abroad buying clubs in Spain.
"They are coming to Spain and I don't like this but it's happening.
"They have [bought] Malaga and Santander and some other clubs; my question is where we go and if this fair on the associations when these clubs can increase capital with no limits."
Rosell said the clubs were the only ones losing out financially in football.
"FIFA and UEFA and the national associations are earning more and more money, you have the players' agents and the players earning more money, but the clubs every year are losing more money. Something is wrong with the equation."
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