Ole Gunnar Solskjaer made the Englishman his first-choice No. 9 after succeeding Jose Mourinho as manager back in December, and Rashford flourished:
Lukaku's £74 million exit to Inter Milan on Thursday had been long expected, but it effectively guarantees Rashford will lead the line for United in the new season, potentially flanked by Anthony Martial and 17-year-old Mason Greenwood.
There are some concerns United do not have enough goals in their squad after opting against replacing Lukaku:
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'Rashford, Martial and Greenwood - are they really number 9s?' Paul Scholes told @RobbieSavage8 he thinks #MUFC might struggle to score enough goals this season. 📻 @RobbieSavage8 Premier League Breakfast podcast - https://t.co/U2xpV1k1JI #SavageSocial https://t.co/AxL4proLT8
But Rashford has said he is ready to take on more responsibility as the leader of the attack, per Michael Kelleher of Sky Sports:
"For me it's just about becoming the guy that's responsible and reliable. I feel like that's the next step for me. Everything goes in order of the way it should be done. I remember these similar steps when I first went into the Under-18s and it takes you a season to grow into that standard of football. Before you know it, you're one of the leaders there and you take responsibility on the pitch. Now I'm in that situation for the first team."
Rashford has now been a first-team regular for three-and-a-half seasons at Old Trafford, but he is still only 21.
He scored 10 Premier League goals in 2018-19, the first time he had reached double figures for an English top-flight campaign.
By contrast, Lukaku netted 12 goals last term to make it seven seasons in a row he had reached double figures in the Premier League, and few players have been more prolific than him in that period:
The 26-year-old also scored at a quicker rate than his team-mate in 2018-19, netting every 178 minutes compared to Rashford's 235 minutes per league goal.
If United are to have a chance of breaking back into the top four in the new campaign, Rashford will need to be more prolific, and he will be eager to open his account in the season opener at Old Trafford against Chelsea on Sunday.