Bruno Fernandes, Lisandro Martinez, Harry Maguire and Luke Shaw will be out of contract at Manchester United by the end of the season.
United have the option to extend Fernandes' contract by 12 months. The midfielder has made a mixed start to the new campaign, but he broke the Premier League assist record last term.
Fernandes is still viewed as United's most important player, and talks have been opened to offer him a new deal.
Fernandes played through a knock in United's games leading up to the international break, and the issue was serious enough to force him to miss Portugal's clash against Norway in the UEFA Nations League last week.
Defensive duo under contract scrutiny
United have the option to extend Martinez's contract by a year. The defender was on the bench for the opening game of the season against Hull after returning late to pre-season due to the World Cup, but he has started all five of United's league games since.
Martinez scored an own-goal against Fulham before the international break, with the ball ricocheting into the back of the net after an initial save from Senne Lammens.
Michael Carrick has continued to pick Martinez and Harry Maguire as his first-choice centre-back partnership this term, but Maguire is another player technically out of contract at the end of the season.
In April, Maguire signed a new one-year contract with the option to extend by 12 months, meaning United have breathing space with both of their first-choice centre-backs.
Shaw's future at the club
However, United will have to offer Shaw new terms to extend his stay at the club, as there is no 12-month extension option in his deal.
Shaw is now the longest-serving player at United, having reached the 12-year anniversary of his £30million transfer from Southampton in June, which made him one of the most expensive teenagers in the world.
The 31-year-old started every Premier League game for United last season, becoming just the fifth player to do so, but he stayed fit as the Reds played their fewest matches in a season for 115 years due to their failure to qualify for Europe.
Although Shaw has already missed three games this season after picking up a small issue, he started against Fulham before the break. United did not sign a left-back over the summer despite exploring targets in that position, but they will prioritise strengthening the position next summer.
