He will be available for selection for this weekend's Celtic League quarter-final against Edinburgh Rugby.
Allen's return to fitness will relieve Cardiff management team headaches as fellow centre Pieter Muller recently injured his calf in training.
However, Cardiff will not be able to select Gary Powell.
The prop injured two discs in his neck and requires surgery.
Hooker Greg Woods is also unavailable following news that the rib cartilage damage sustained in a training match last Friday, will keep him out of action for up to a month.
Cardiff will announce the team to travel to Scotland on Wednesday.