Disgruntled Premier League managers could ask for the reintroduction of five substitutes this season despite the concept being rejected twice.
A growing number of managers say they are dissatisfied at the return to three for 2020-21, after five were brought in for Project Restart in June.
The Premier League is the only major competition to return to three.
Leading managers believe the current substitution limit is contributing to injury problems.
Liverpool boss Jurgen Klopp and Manchester City counterpart Pep Guardiola have both said the decision is partly responsible for a spate of muscular injuries across the top flight.