Christopher Morrison attacked the child in the Asda store in Clydebank, West Dunbartonshire, on September 18 last year.
Morrison was captured after his DNA linked him to the crime. He pled guilty to the sex attack when he appeared at the High Court in Glasgow last December.
Morrison, of Elderslie, Renfrewshire, was due to be sentenced yesterday, but Judge Lord Bracadale called for a further assessment.
One option could see the 20-year-old made the subject of an Order for Lifelong Restriction.
Morrison – who was remanded in custody – will return to the dock in May.