Rashford developing quicker than Ronaldo did – Southgate
Rashford scored in England's matches against Spain and Switzerland, moving onto five international goals.
But the 20-year-old has battled for starts at United, making just one so far this season, while he was sent off against Burnley earlier this month.
Southgate praised Rashford's development, comparing him to Juventus star Ronaldo – who was at the beginning of his United career at the same age – and Tottenham forward Harry Kane.
"He is [a special talent]," he told UK newspapers.
"We have to remember that I don't think Harry, at that age, had hardly played anywhere near the matches for Spurs, really.
"Even if some of those other top players who have broken into the team, some of the step-overs and things Ronaldo was doing at that age, but he wasn't converting them into the number of goals, so we have got to give him time to develop.
"He [Rashford] has still played a lot of football, although maybe not the continuous starts and I'm really pleased for him that he leaves England full of confidence. He's got huge competition for places at his club, so you can understand [his frustration]."
Clinical from @MarcusRashford! #threelions pic.twitter.com/pVvct0SHfb
— England (@England) September 12, 2018
Rashford has managed double digits in goals the past two seasons, while Ronaldo first achieved that feat in 2005-06, as he turned 21.
The first time Kane struck more than nine in a campaign was in 2014-15 – as he approached 22 years of age – but he netted an impressive 31.
Despite Rashford's frustration with a lack of starts at United, Southgate said his club manager Jose Mourinho was a huge fan.
"It's not my business to interfere with club managers, they have a difficult job to do and they have big squads at the top six, huge competition for places, so Jose thinks the world of Marcus," he said.
"He's a huge admirer of him, but he's got his job to do."