The young duo have barely featured for Villa over recent months due to lengthy injury layoffs.
Grealish has played twice for Villa’s Under-21s since returning from a lengthy ankle injury earlier this month and made his first-team comeback as a late substitute in last weekend’s 2-1 home defeat to Bournemouth.
The 20-year-old midfielder also helped create two goals for the U21s in Monday night’s 3-2 home win over West Ham United, although he was forced off during the latter stages of the game after picking up a knock.
However, having trained fully since, the homegrown playmaker should be fit and available for Saturday’s trip to Old Trafford.
Adama, meanwhile, also started the U21 matches against West Bromwich Albion and West Ham this month and came on for the final 20 minutes of the Bournemouth clash before Grealish’s introduction.
The pacey winger had previously been sidelined for three months after breaking his foot during January’s 3-1 loss at Sunderland, but he could now be in line to earn just his first Premier League start for the club since his summer move from Barcelona this weekend.
"They have trained very, very well. I couldn't fault them,” Black told avfc.co.uk on Grealish and Adama. "There are a lot of players who have trained well this week so I will have to make a judgement on Adama and Jack.
"There will be competition - even competition for places on the bench. That's pleasing."
Villa currently sit 15 points from safety at the foot of the table with only three league wins and are all but certain to be relegated for the first time since 1987 with just five matches remaining.
They could already be down by the time they face United on Saturday if Norwich City avoid defeat at home to Sunderland in the lunchtime kick-off, but Black insists that his side will not just lie down and accept their fate.
“I can’t allow that to happen,” the Scot said at his pre-match press conference. “I’ve got to come and work here every day. Yeah, the circumstances are what they are, but we’ve got to try and be as positive as we can and try and get the maximum.
“All I’m trying to do in any small way is put something back into the club that pushes it into another direction, and that’s all I’m focused on.”