Johnson has struggled to make an impact at Craven Cottage since joining Fulham from Kansas City Wizards in January.

He had been a regular scorer in Major League Soccer, but failed to find the net in six Premier League appearances last season.

The United States international was not involved in last week's 2-1 defeat at Hull City and has now been allowed to move to Ninian Park.

Fulham have the option to recall the 24-year-old in January, while Cardiff boss Dave Jones hopes he has recruited another quality signing.

Jones said: "Hopefully we've picked up another good player that will come in and help the cause."

Cardiff have been looking to improve their attacking options over the summer after seeing Jimmy Floyd Hasselbaink and Robbie Fowler leave.

Jay Bothroyd and Ross McCormack have arrived in South Wales and now Johnson has been added to the squad, with the striker set to make his debut in the Carling Cup against MK Dons next Tuesday.