Need to bleed the slave cylinder to get the air out of the line. Its probably leaking too since the fluid is low in the first place, so it would be a good idea to replace it. Unfortunately IIRC the slave cylinder is INSIDE the bellhousing in the newer models. So replacement will require removal of the transmission.
There should be a dust cover on the bottom half of the bellhousing. Unbolt it and check inside to see if there is clutch fluid splattered everywhere. If there is, its a good bet the slave cylinder is bad.