Proposals to close the Premier League and English Football League summer transfer windows before the start of the season next year are "a long way off", says a leading sports lawyer.
The current window, in line with many other European leagues, closes on 31 August - almost three weeks after the start of the Premier League campaign.
Both the Premier League and EFL will discuss potential changes next month.
"There are problems down the line," lawyer Chris Farnell told BBC Sport.
"I don't think the way they are looking at it would be smooth. It would be fraught with problems and potentially legal challenges."
Farnell, the lead lawyer on the sale of Swansea City last year, said he was unsure whether football's governing body Fifa would even allow the changes to be made.
"I think it is something that has been raised off the cuff by one or two managers.
"It needs to be better thought out, better planned and prepared and I think it is a long way off happening yet."
A vote is set to take place at the next Premier League shareholders meeting on 7 September, while the EFL will also table the matter for discussion next month.
The EFL said clubs had already expressed the opinion that closing the summer window at the start of the season "would be an improvement on the current position".
A spokesman added: "It will be important that all the consequences of such a decision are fully considered, as the requirements of our clubs are different to those in Europe's top flight leagues."
What do Fifa regulations say?
Players may only be registered during one of two annual registration periods. In Europe these are the summer and January transfer windows and are fixed by each individual national association.
The first window begins once the season has finished and must not exceed 12 weeks. The second, which usually occurs mid-season, must not exceed four weeks.
For the Premier League and EFL, Fifa regulations state the transfer window should close no later than 1 September, or as near as practical if it clashes with a weekend.
However, players whose contracts have expired prior to the end of the transfer window may sign for another club outside the registration period.
As leagues in confederations around the world start and finish at different times, so do their transfer windows - for example, the USA's first window began on 14 February this year and ended on 8 May, while China's opening registration period ran from 1 January to 28 February.
BBC Sport's Simon Stone
As with all issues affecting the Premier League, it will need 14 clubs to vote in favour before any change can be made.
It is a complicated scenario, not least because it has the potential to put England's top-flight teams at a disadvantage because rivals across Europe will be active in the market for up to three weeks after the Premier League window has closed.
The plan would have no power to prevent a club such as Barcelona targeting Liverpool's Philippe Coutinho - as they have done this summer - for instance.
As Europe's major leagues all start at different points - France was a week before England, with Spain, Italy and Germany a week after - a Europe-wide change is not going to happen.
There is also the potential for clubs who do not agree - Watford are said to be against it - or agents to mount a legal challenge.
However, the disruption caused by the continuation of the transfer window beyond the start of the season has become so great, and started to affect so many teams, the feeling that something has to be done has begun to take hold.
What do Premier League managers say?
Liverpool manager Jurgen Klopp and Swansea boss Paul Clement are among those to have called for a change.
Klopp was without playmaker Coutinho for Liverpool's Premier League opener against Watford, and midfielder Gylfi Sigurdsson was absent for Swansea's game at Southampton.
"An earlier transfer deadline day would have helped us this year. In general, it makes sense that when the season starts that the planning is over," Klopp said.
Clement added: "A better situation would be if the transfer window closed before the start of the season.
"I don't really understand why it goes to the end of August. I know there's talks about that changing in future. That's my opinion that it should do."
According to research from betting company Bwin, seven of the 10 biggest transfers in the past five seasons which have been completed after the league campaign started involved Premier League clubs.
They were Gareth Bale to Real Madrid, Angel di Maria and Anthony Martial to Manchester United, Kevin de Bruyne and Nicolas Otamendi to Manchester City, and Mesut Ozil and Shkodran Mustafi to Arsenal.
The Premier League makes 24% of its signings after 15 August, while 12% of its signings are on transfer deadline day.
Last season's runners-up Tottenham typically make their signings late in the transfer window, and Bwin says 47% take place after the season starts.