Manchester United and Man City have both been active in the January transfer window and have just a few hours left to improve their squads before the transfer window slams shut.

Manchester United approached the final day having let Marcus Rashford leave Old Trafford for Aston Villa on loan, with a £40million option to make the move permanent in the summer. The Reds also finalised a deal for Leece wingback Patrick Dorgu on Sunday in the region of £29million, with Ayden Heaven also bolstering Ruben Amorim's ranks.

City on the other hand have been one of the most active sides in the Premier League and are still hopeful of bolstering their squad before the deadline at 11pm this evening.

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If United or City are tempted into any late business, they may need to acquaint themselves with a transfer deal sheet. But what are they and why are they so important?

What is a transfer deal sheet?

As mentioned, the window closes at 11pm UK time. To confirm that a deal for a player has been agreed before the market closes, a transfer deal sheet must be filled out to allow for more time to thrash out any last minute details. The concept was introduced to the Premier League in 2008.

Due to the hectic nature of Transfer Deadline Day, some clubs have mere minutes to fill out the document and ensure the move can take place.

Once submitted, the clubs have an additional two hours to get any potential signing over the line if the sheets are completed correctly. Failure to dot the I's and cross the T's before the two-hour extension renders any deal invalid.

The information on the sheet itself is simple - signalling which player will be making the switch, the clubs they are moving to and from, the transfer or loan fee and any other potential add-ons.

What role does the Premier League have in a transfer?

In order to register a player, clubs have to send the Premier League all documents relating to the transfer, including the contract, the transfer agreement, permission to work in the UK, if required, international clearance if transferring from abroad as well as any transfer levy that may apply.

According to the Premier League, officials from the competition will approach clubs as the deadline approaches to ask whether they are planning to complete any business so that the Premier League's Football Operations and Regulatory departments are prepared.

The league's office is staffed up until the 11pm deadline should any queries from clubs come.