Manchester United striker Romelu Lukaku is already making headlines for a last-minute transfer to Inter Milan, with Brazil international David Luiz touted to make a move from Chelsea to Arsenal.
Teams will scramble to fill important positions in their squads and increasingly desperate players will push for a move by 5pm on Thursday.
But one thing every single club will take great pains to be certain about amid the panic is the player’s health and fitness.
As Burnley’s club doctor Simon Morris told the Premier League recently: “If you’ve got enough money to buy an expensive sports car, you’d want to look under the bonnet, wouldn’t you?”
But what really happens during a player medical? Here are the roughly four hours’ worth of steps that football clubs generally follow.
The blood test
Typically the first hurdle for any footballer to overcome will be the blood test.
Doctors look up hundreds of variables to check if there are any underlying infections or any conditions that may pose a problem now or in the near future.
Medics will check if players show any signs of anaemia, for example, and to look at what their kidneys or livers are like.
Sugar levels, and the thyroid gland are also inspected before a urine sample is taken to find if there are any abnormalities.
The blood test could start at, say, 8am and the entire medical won’t be over until close to midday.
Another test clubs will run early doors is a thorough and full examination of the heart.
This involves an ultrasound to look at the structure of the heart as well as an electrocardiogram (ECG), which is a simple test to check its rhythm and electrical activity.
You may have seen clubs sharing pictures of players hooked up to sensors attached to their skin – there’s a good chance that will be the ECG test.
Doctors will also check on their height and weight as well as their blood pressure before going through a detailed questionnaire to establish any problems within the player’s family.
How they move
Once all the tests focusing on the player’s organs and bodily functions have been completed, it’s time to check on the joints and muscle movements.
The medical team will look into specific bits – like the joints, the ligaments, the soft tissue and muscle supporting the ligaments and joints – but what’s crucial is how the player moves.
Alasdair Beattie, head physiotherapist at Burnley, said: “We can look at things individually but we want to see how [the player] moves as a person, landing strategies, that sort of thing.
“What’s called disassociation – can he move one part of his body while keeping other bits stable? Which is obviously vital to the job that he does.”
They will also be a sprint test or general running or movement-based exercise to gauge the player’s current fitness – this is when the player breathes into tubes, typically on a treadmill.
The MRI scan
Up to now, the medical is two hours old but we’re only halfway through.
The MRI scan is probably the most tedious part of the medical for the player, who can expect to lie still in a loud MRI machine for up to two hours.
For outfield players, the scan focuses on the back, hips, knees and ankles, while goalkeepers will have a scan on their shoulders too.
The medical team then prepares a report with results and any warnings (if needed) to pass on up the club hierarchy.
Once that’s done – barring any worrying results of discoveries – the player and the club are free to sign on the dotted line.