United's second successive loss after their League Cup exit at Tottenham on Thursday underlined Ruben Amorim's belief that their road back to the top will be long and arduous.
The Reds sit five points clear of second-placed Chelsea, who can close the gap with a win against Brentford at Stamford Bridge on Sunday.
Premier League leaders Liverpool's Merseyside derby trip to Everton on Saturday was postponed due to adverse weather conditions caused by Storm Darragh.
Nottingham Forest were furious not to be awarded three penalties during a 2-0 defeat at Everton in April as they battled to preserve their Premier League status.
Manchester City's second successive draw in the league was especially frustrating as Arsenal moved level on points with them with a last-gasp 4-2 win against Leicester a few hours later.
Onana is expected to replace Douglas Luiz, who left Villa for Italian Serie A side Juventus earlier.
Arsenal had been almost flawless in 2024, with 16 wins and one draw, away to City, in their 18 league matches.
Manchester City became the first team to win four Premier League titles in a row after beating West Ham United 3-1 at the Etihad Stadium on Sunday.
Premier League Final Day Live Streaming: The Premier League title will be decided on the final day of the season with both Manchester City and Arsenal still in the race.
Elijah Adebayo kept Luton in the hunt to avoid relegation from the Premier League as his equaliser rescued a 1-1 draw against Everton on Friday.
Everton secured their first win in a Merseyside derby at Goodison Park since 2010 to leave Liverpool's Premier League title aspirations in ruins after a 2-0 defeat on Wednesday.
Cole Palmer scored four goals to put Chelsea within touching distance of the Premier League's top six after a 6-0 win over Everton on Monday.
The Premier League said on Monday a speeded-up, "expedited" process will be put in place after Everton appealed against a two-point penalty imposed on the club for breaching financial regulations.
Tottenham missed the chance to move into the Premier League's top four after a 1-1 draw at West Ham, while Newcastle were also held 1-1 by Everton on Tuesday.
Premier League strugglers Everton revealed an 89.1 million pounds ($112 million) loss for the 2022-23 season in their latest financial accounts on Sunday.
Manchester United kept alive their faint hopes of finishing in the Premier League's top four with a 2-0 win against Everton, while Arsenal prepared for their chance to seize top spot later on Saturday.
Premier League strugglers Everton salvaged a 2-2 draw with Tottenham thanks to Jarrad Branthwaite's last-gasp equaliser, while Aston Villa moved into fourth place with a 5-0 demolition of Sheffield United on Saturday
Forest survived a scare to beat third-tier Blackpool 3-2 after extra-time, while Everton were 1-0 winners against Crystal Palace in another of the night's third-round replays.