Spanish clubs have until 2 September to complete their transfer business and there is still the possibility of incoming and outgoing activity at Atletico Madrid.
Atletico, which begins its campaign with a home match against Getafe on Monday (AEST), has been strongly linked with Valencia forward Rodrigo and Angel Correa is among those to have been tipped for the exit.
Simeone said he wants LaLiga to follow the example set by the Premier League in moving the cut-off point for new signings as it would be "mentally healthier" for teams.
"I think all the managers would love it, like it happens in England," he said.
"If I am not wrong, all of them have the squad built when the competition starts.
"It would be mentally healthier for everyone being focused on the guys who will play. Now we have to wait until September 2 as there can be updates."
Atletico appeared to be on the brink of signing Rodrigo from LaLiga counterpart Valencia earlier this week, only to pull the plug on a deal reported to be worth €60 million ($99.3 million).
Valencia general director Mateu Alemany revealed the original offer is "no longer on the table", but Simeone was unwilling to comment on the transfer saga ahead of the meeting with Getafe.
"You should ask to Andrea Berta, Miguel Angel [Gil Marin] and Enrique [Cerezo]," he said. "I am just focused on Getafe, a team who did a fantastic season last year."
Correa's future is also uncertain on the eve of the new season amid links to AC Milan, although that deal could depend on Rodrigo joining Atletico as a replacement.
Asked if Correa is part of his plans, Simeone said: "I would like all the good players to stay. I would also like to sign all the good players and build the strongest team possible to compete as the team has competed so far."
Koke, Saul Niguez, Jan Oblak and Jose Gimenez have been installed as Atletico's four captains for 2019-2020 after the departures of Diego Godin, Juanfran and Antoine Griezmann during the close season.