It has been the Red Devils’ worst start to a league season since 1992/93.
The additions of Sanchez and Fellaini are part of three changes made to the side that lost 3-0 at home to Tottenham, with Victor Lindelof also coming back in. Anthony Martial and Eric Bailly are back on the bench after missing out on the Spurs defeat.
Manchester United defender Luke Shaw has been handed an England recall.
The 23-year-old has not played for his country since a 1-0 defeat to Germany in 2017 but has returned at the expense of Old Trafford team-mate Ashley Young in the Three Lions’ first squad since the World Cup.
Uncapped Southampton goalkeeper Alex McCarthy is included with Burnley’s Nick Pope injured, while Joe Gomez and James Tarkowski also return for the Nations League game at Wembley against Spain on September 8 and friendly in Leicester with Switzerland three days later.
Shaw has impressed early in the season for United, including scoring his first ever senior goal in their season-opening win over Leicester.
Manager Gareth Southgate said: “He has had a difficult period adapting to a new club, a horrendous injury, but he has had an extra edge to his game.
“When it’s been going against his team he has been one who has shown aggression and a desire not to lose.
“I’m really pleased for him that he looks like he’s playing with confidence.”
Southgate has also given Adam Lallana a recall after the Liverpool midfielder was left out of the World Cup squad following an injury-plagued campaign.
Jamie Vardy and Gary Cahill have effectively retired from international football – although are available in case of an injury crisis.
In Vardy’s absence Southgate named Harry Kane, Marcus Rashford and Danny Welbeck as the only strikers in the squad.
Midfielder Ruben Loftus-Cheek keeps his place after impressing in Russia in the summer, despite playing just 22 minutes for Chelsea this season.
Southgate said: “We’re on the back of a successful tournament. Not too much can have changed in that time because we reached the semi-final and there has only been three league games.
“We had some mature conversations with Jamie Vardy, Gary Cahill and Ashley Young in terms of the desire to look at younger players.
“We had five changes anyway and we felt that was enough. We also won’t stand still.
“Luke Shaw is still only 23, Joe Gomez is 21 so we have lowered the age again. We are aware of the excitement around other young players but it might be a bit too early for some.”
The 22-year-old has been offered the new contract despite his public feuding with manager Jose Mourinho, which has led to reports he could be ready to leave Old Trafford.
But Martial will now sign the deal, as he believes he will last longer at United than the increasingly under-pressure Mourinho.
The Frenchman joined the club from Monaco in 2015, for a transfer fee of £36million – then a world-record for a teenager – that could rise to £57million with add-ons.