The 29-year-old winger Amrabat has not played for the Hornets since suffering a ligament injury in his left ankle in the 4-1 defeat to Tottenham Hotspur on 1 January, which also ruled him out of Morocco's Africa Cup of Nations campaign.
He was permitted to travel to Netherlands to undergo treatment in January before returning to London Colney last week, with the club's medical director Luca Gatteschi believing the player is still a couple of weeks away from a return to the first-team.
The ankle is good, it's stable," Gatteschi told the club's official website. "We need to look at the reaction when it has load on the pitch. This week will be a week of rehab on the pitch, rehab in the gym. He will have a progressive load on the ankle and then we will see the reaction."
Zuniga, who was on target for Watford in their 3-1 victory over United at Vicarage Road last September, has also been absent with an ankle injury, returning to the club last week having spent some time recuperating back home in Colombia.
Belgian midfielder Kabasele meanwhile has missed the last three games but is back in full training. "He had an old muscle problem and so we took time to strengthen the quad muscle and the knee," Gatteschi explained. "He needed time to reduce the future risk of injury so he had two weeks of training and rehab work on his thigh."
Jose Holebas meanwhile missed training earlier this week as a result of a challenge from Jeff Hendrick that saw the Burnley midfielder sent off in the opening six minutes of the Hornets' win last Saturday.
"He had a contusion on his calf," Gatteschi added. "Thankfully there is no muscle injury but we had to avoid putting load on the calf as a consequence of the kick he got in the first-half."