Marcus Rashford is urging NHS workers to do their bit to help low income families get the support they need to feed their children.
In an open letter in the British Medical Journal (BMJ), the footballer says more than 40% of households entitled to claim Healthy Start vouchers have not signed up – potentially because they are not aware it exists.
He expressed concerns that numbers are plateauing due to a lack of awareness.
Healthy Start is a NHS-run food voucher scheme that pays coupons to pregnant women or low income families on benefits with children aged under four.
In Scotland, the £8.50 a week voucher initiative is known as known as Best Start Foods.
Those who qualify receive vouchers to buy basics like fruit and vegetables, and can also be redeemed against milk, formula for babies and vitamins.
Writing in the BMJ, Rashford says his Child Food Poverty Taskforce – to get free school meals to vulnerable children during the school holidays - has pushing for more awareness of Healthy Start.
Find out if you qualify for Health Start vouchers and how to apply, here.
He said: "More than 40% of those eligible for the vouchers are still not registered for the scheme, and I'm confident that the majority of these parents can be found in communities just like mine, where I grew up - no internet, no high street, no word of mouth."
Rashford argues health professionals need to do more to ensure all those who are entitled to apply know about it "especially given the planned digitisation of the scheme this autumn, which will disproportionately disadvantage those without easy access to the internet," he said.
He wants staff to use an online eligibility calculator and "consider collaborating with us on communicating and educating people about the scheme when possible".
The Manchester United striker famously forced the government into an embarrassing U-turn last year, after launching a campaign for free school meals to be available over the six week summer break.
After rejecting proposals, the prime minister said they had to understand the pressure families were under and agreed to extend the scheme at the eleventh hour.
Labour's shadow child poverty secretary, Wes Streeting, said the measures did not go far enough and "more and more children are living in poverty under the Tories".
It comes as the government prepares to withdraw £20 a week from millions of Universal Credit households.
He said: "With no government strategy for lifting children out of poverty, once again we see Marcus Rashford having to do the government's work for them.
"If Boris Johnson is out of ideas for what to do, he should implement Labour's Children's Recovery Plan to provide immediate support for all children to catch up on lost learning following the pandemic."
Earlier this year, Rashford launched an initiative with Michelin starred chef Tom Kerridge, which the footballer said he hoped could help remove the kind of "embarrassment" his mother had felt when using food banks.