The current top four leagues in Europe -- according to UEFA's coefficient rankings
-- are the Spanish La Liga, German Bundesliga, English Premier League and Italian Serie A.
Under the present system, La Liga, the Bundesliga and the Premier League are guaranteed three places in the group stage, with a fourth spot possible through the playoff round, while Serie A is sure of two places and a third available through the playoff round.
France's Ligue 1, Russia's Premier League and Portugal's Primeira Liga sit fifth, sixth and seventh respectively in UEFA's coefficient rankings, although they currently remain some distance behind the top four divisions.
The new changes mean that 16 of the 32 Champions League group-stage spots will now be guaranteed to teams in Europe's top four leagues.
The announcement comes just a day after UEFA presidential candidate, Aleksander Ceferin, warned that a potential breakaway league of Europe's top clubs could lead to war
between teams and the governing body.
UEFA chief of communications and media, Pedro Pinto, told CNN Friday that the changes will help to create a better Champions League for all involved.
"The amendments are sound, in the best interests of European football and will make the tournament stronger," Pinto said.
"We now have four group-stage spots from the top four leagues, which means we believe that we're increasing the sporting value of the competition, which will then increase the financial value of the competition."
"This competition is as inclusive as it's always been," Pinto added. "Giving four group-stage spots to the top four leagues will help improve the sporting and commercial interest of the competition, so we can then spread the money across the competition and throughout all clubs."
'Evolution not revolution'
As part of its "evolution of UEFA club competitions" process for the 2018-21 cycle, UEFA also announced that financial distribution to clubs participating in the Champions League and Europa League will be "increased significantly."
"A new four-pillar financial distribution system (starting fee, performance in the competition, individual club coefficient and market pool) will see sporting performances better rewarded, while market pool share will decrease," the governing body confirmed.
UEFA also announced that a new system for club coefficients, which help determine its coefficient rankings, will also be implemented with teams in future being judged on their own records and historical success in Europe also being taken into account.
Elsewhere, Europa League winners will automatically qualify for the Champions League group stage from the 2018-19 season, rather than having to first take part in the playoff round.