Leeds boss Uwe Rosler has been looking to bolster his midfield options all summer and he has moved quickly to land Adeyemi after seeing Luke Murphy ruled out for the start of the new campaign through injury.
Rosler is a big admirer of Adeyemi having worked with the midfielder during his time in charge of Brentford when he signed the midfielder on loan from Norwich City.
Adeyemi joined Cardiff from Birmingham City last summer and he started the season as a regular under Ole Gunnar Solskjaer, but found himself relegated to the bench under Russell Slade.
A number of clubs have expressed an interest in Adeyemi with Cardiff willing to offload him to try and trim their squad and wage bill.
If Adeyemi impresses during his loan stint at Elland Road, Leeds have the option to make the move permanent and there is no recall clause in his loan deal from Cardiff.