When you have found a player you want to buy, offer

as much as you can for the player or enough for the

club to accept your offer. When it comes to offering

the player a contract, click at the very top of the 

screen where you choose whether he is indespensible 

to the squad or used in rotation etc. Click at the 

top of that screen where it says the player's name 

and then go to the top corner and withdraw your bid 

for him and straight away approach to buy him again 

for £0 or however much you want to spend. Then press

either back or continue game and it will go back to 

the offer contract screen and you then just carry on

as normal and you get a player for free!