Williams has been sidelined since September with an ankle injury, but the Wales international is back in contention after coming through 45 minutes of Palace under-21s' clash against QPR unscathed this week.
Fellow winger Jerome Thomas is a doubt after picking up a groin injury in training, while club captain Paddy McCarthy remains out with a long-term groin problem.
Millen has been in charge on a caretaker basis for almost a month since Ian Holloway departed, but revealed on Thursday that he expects Saturday’s clash at the KC Stadium to be his last at the helm.
Tony Pulis is reportedly set to take over at Selhurst Park and the former Stoke City boss will have a big job on his hands should he take the job.
Palace are bottom of the table without a win in their last eight games, scoring only two goals in the process.
They did stop the rot after seven successive defeats by drawing 0-0 at home to Everton before the international break, though, and Millen's side can also take heart from the fact they have not lost to Hull in their last six meetings.
However, Millen knows the London club can expect another stern test against Steve Bruce’s team, who were promoted from the Championship last term along with Palace and Cardiff City.
"Hull have probably adapted quickest out of the three teams that have come up and we've got to play catch up," he said.
“We know it's going to be a tough game. They are a difficult team to read in terms of their shape, but we've got to concentrate on us.”
Hull are boosted by the return of goalkeeper Allan McGregor (thigh) and winger Robbie Brady (hernia), while Robert Koren is in contention for a start after being on the bench in the 4-1 defeat at Southampton last time out.
It remains to be seen whether defender James Chester will be return after a hamstring injury.
Bruce’s side boast an unbeaten home record in the Premier League this season, and have not conceded a goal in their last four games at the KC Stadium in all competitions.
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