That’s according to Sky Sports pundit Gerry Francis.
Lukaku and Matic joined United in the summer for a total fee of £115m.
The former Everton star has netted seven times in as many Premier League games, while Matic has commanded United’s midfield.
And Francis says the duo have turned the Red Devils’ fortunes around.
“I think two key players for me (have been the difference),” he told Sky Sports.
“That’s been Matic, who’s been vitally important for organising in front of the back four, winning the ball back, similar to what (N’Golo) Kante has done for the last two seasons for Leicester and Chelsea, and Lukaku up front.
“He’s given them that little bit of extra pace in behind, proven goalscorer in the Premier League.
“Even if Lukaku gets injured they can use (Marcus) Rashford in that role.
“There is a lot more strength in depth at the highest level and obviously that has been shown by their results.”
And when asked who is more important to United out of Lukaku or Matic, Francis voted for the midfield powerhouse.
“I think they can afford to lose Lukaku more than Matic because I don’t think there is a similar replacement to Matic,” he added.
“I think Rashford can do exactly the same as Lukaku and will do as his year and his season progresses.”
