Colum Martin was caught with three of the smoke grenades during a search outside McDiarmid Park in Perth shortly before a Celtic match last season.
Martin - who already missed watching his team lift the league title under a strict bail condition - will also now miss several matches at the start of the new season.
He was banned from attending any SPFL match prior to being sentenced for the offence when he returns to Perth Sheriff Court on 3 August.
Martin, 24, from Motherwell, initially spent a night behind bars after his arrest before appearing from custody at Perth Sheriff Court in December last year.
He admitted trying to enter McDiarmid Park in Perth on 13 December while he was in possession of controlled items, namely three smoke grenades.
A second charge of having cocaine at Perth Police station on the same date was dropped by the Crown yesterday and sentence was deferred for reports by Sheriff Fiona Tait.
Fiscal depute Tina Dickie told the court: “The St Johnstone v Celtic match was due to take place at McDiarmid Park. Security staff were standing outside the turnstiles.
“They stopped the accused as he was about to enter because they suspected he was in possession of some kind of controlled item.
“From his coat pocket was recovered a small black container, a smoke grenade. Police were called over and they found a further two inside his coat pocket.”
Sheriff Tait continued the case for reports and the bail condition preventing Martin attending any SPFL match was also kept in place.