As revealed by Millwall Mad earlier this week, The Lions were in discussion with the Yorkshire club over the player after U's boss Gary McAllister decided that the Democratic Republic of Congo striker was no longer part of his plans for next season.
Jackett was keen on signing Kandol on a permanent basis but the length of his contract and the size of his wages proved to be a stumbling block.
The 27-year-old London born striker hit 11 goals for Leeds last season and will go straight into the squad for Saturday's game against Oldham Athletic.