Former England manager Hope Powell says a Women's Super League of more than 12 teams would "dilute the talent and quality" of the division.
Brighton boss Powell will lead the club in the top tier next season after their application was accepted in December.
This season's WSL contained 10 teams but that could be increased to as many as 14 sides for the 2018-19 campaign.
Asked about a possible 14-team league, Powell said: "I'm not sure - 12, maximum, might make it competitive."
She told BBC Radio 5 Live: "If you stretch it any further than that, you start to dilute the talent. And the quality of games.
"The league will be divided even more so."
Part-time side Yeovil took 15 games to score their first WSL goal this season, and finished bottom of the table with just two points.
Clubs including West Ham United have stated their desire to join the top tier, with successful applicants being named by the FA at the end of the month.
"I think it's something the FA have to consider and allow the other parts of the game to catch up," Powell said.
"Increase that talent pool lower down and then, in the future, hopefully you'll be able to expand that league further."
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