A club can start discussions with any player whose deal is within six months of expiring - providing they are in a different domestic league to their transfer target.
For example, Manchester United could negotiate with a La Liga player who has a contract expiring at the end of June, but not someone in the Premier League who might be in the same boat; it must be the final month of the deal to attempt to sign players from the same domestic league.
Here, Flashscore takes a look at the best potential free agents for each position in 2026.
Goalkeepers
Several high-profile goalkeepers are nearing the end of their current deals, with AC Milan's Mike Maignan the most prominent name on the list.
The Frenchman is a regular starter for both his club and the French national team, and is currently an important component of a Milan side challenging for the Serie A title - meaning a renewal could be likely, although several top clubs could be keeping an eye on his situation.
A trio of Premier League goalkeepers also have deals up in 2026: Nick Pope (Newcastle), Stefan Ortega (Manchester City) and Illan Meslier (Leeds).
Also, keep an eye on the situations of veteran shot-stoppers Manuel Neuer and Yann Sommer, who are into the final six months of their deals at Bayern Munich and Inter.
Right-backs
Real Madrid's Dani Carvajal is the biggest name out of contract at right-back, although he barely featured after suffering an injury at the end of October.
At 33 years old, coupled with the arrival of Trent Alexander-Arnold and the versatility of Federico Valverde, Carvajal's future could be one to keep an eye on.
Fellow Spaniard Oscar Mingueza's deal is also up in June, although his current club Celta Vigo are reportedly confident of renewing.
Former Liverpool and current Wolves defender Ki-Jana Hoever could also be available.
Central defenders
A whole host of central defenders reportedly have contracts expiring in 2026, with the position set to be the source of several transfer merry-go-rounds.
Marc Guehi (Crystal Palace), Ibrahima Konate (Liverpool) and Dayot Upamecano (Bayern Munich) are all approaching their prime years, although the latter is said to be in negotiations to extend with Bayern.
Guehi and Konate have been at the centre of transfer speculation for some time and their next moves could directly impact each other.
Elsewhere, veteran stars like Madrid's Antonio Rudiger and David Alaba, Barcelona's Andreas Christensen, and England duo John Stones and Harry Maguire could all be available.
Other potential free agents include Stefan de Vrij, Kalidou Koulibaly, Michael Keane and Lewis Dunk.
Left-backs
Plenty of Premier League left-backs are approaching the end of their respective deals, including Vitaliy Mykolenko, Andrew Robertson, Dennis Cirkin, Tyrell Malacia, Ryan Sessegnon and Rico Henry.
The latter three have options to extend by a further year that could be taken up by their respective clubs.
Across Europe, Bayern's Raphael Guerreiro is the biggest name left-back with a contract set to expire in 2026.
Defensive midfielders
The contracts of a staggering number of defensive midfielders are up in the next six months: Casemiro (Manchester United), Yves Bissouma (Tottenham), Vitaly Janelt (Brentford), Jefferson Lerma (Crystal Palace), Thomas Partey (Villarreal) and Martin de Roon (Atalanta), just to name a few.
A host of Saudi deals are also up, including ex-Premier League trio Ruben Neves, Fabinho and N'Golo Kante, as well as former Inter star Marcelo Brozovic.
Both Casemiro and Partey have the option of extending for an extra year.
Central midfielders
Highly-rated Feyenoord midfielder Quinten Timber is set to be a free agent in 2026 and has reportedly drawn interest from Europe's top clubs.
Other potential big-name departures are Juventus' Weston McKennie and Bayern star Leon Goretzka, while Saudi Pro League talent Frank Kessie is also potentially available.
Brentford's Mathias Jensen's deal runs to summer 2026, but the club have an option to extend should they wish to do so.
Attacking midfielders
Manchester City star Bernardo Silva is nearing the end of his deal, although he still features regularly for a club competing across four different competitions.
Another attacking midfielder who could be available is Borussia Dortmund's Julian Brandt - but he has reportedly been offered a new contract.
Matheus Pereira - who enjoyed a solid spell in the Premier League with West Brom - has a deal set to expire at Cruzeiro.
Other noteworthy names include Crystal Palace's Daichi Kamada, Lorenzo Pellegrini of Roma and Fenerbache playmaker Talisca.
Wingers
There's a bit of a lack of potential free agent wingers this year, although the Fulham duo of Harry Wilson and Adama Traore could become available.
Former Liverpool star Sadio Mane is another whose deal will be up - as well as RB Leipzig forward Timo Werner.
Villarreal's Ilias Akhomach is the most high-profile youngster on the list, but he has struggled for regular game time in La Liga.
If looking at players who can play on the wing or across the front line, both Serge Gnabry (Bayern) and Paulo Dybala (Roma) are nearing the end of their deals.
Strikers
Juventus forward Dusan Vlahovic is set to become a free agent in 2026 and is still aged just 25, so he could have plenty of suitors across Europe.
Veteran striker Robert Lewandowski is approaching the end of his Barcelona contract, as are Memphis Depay and Karim Benzema.
Experienced Premier League goalscorers Raul Jimenez and Danny Welbeck could also become available should their clubs not try to negotiate new deals.