Gillislee's teammate LeSean McCoy (knee) has been ruled out for Sunday's game against the Cowboys, Vic Carlucci of The Buffalo News reports.
Karlos Williams is listed as probable, so it looks like Williams and Gillislee will share McCoy's usual workload. The team isn't saying who the starter will be (yet), but Williams, when healthy, has been the backup to McCoy all season and if he's close to full health he'd probably be the slightly better fantasy play. That said, Gillislee has looked great in limited time (14 carries for 146 yards and two scores) and no matter what he'll get his chances Sunday as well.