Aberdeen's hopes of a European scalp had been boosted by the news the hosts were without nine players due to positive Covid-19 tests, with manager Ruben Amorim absent as well because he was self-isolating.

The outbreak saw Sporting's scheduled domestic fixture with Gil Vicente last weekend called off, but the unavailability opened the door for others and one made his mark straight away.

Only seven minutes had been played when the deadlock was broken in Lisbon by 18-year-old Tomas.

After Sporting won back possession, one-time Fulham attacker Luciano Vietto slipped a pass into teenager Tomas and he produced an accomplished finish from inside the area for his first goal for the club.

In spite of a terrible start, Aberdeen responded strongly and Ash Taylor saw a tame header saved before a fine Jonny Hayes run ended with a weak shot on target from an angle.

Ross McCrorie made a lung-busting dribble on the half-hour mark which was ended by Vietto, who received a yellow card for the cynical foul.

The resulting free-kick came to nothing though, and the Scottish side were indebted to goalkeeper Joe Lewis for keeping the score at 1-0 with five minutes of the first half remaining.

A second corner in quick succession saw the ball drop for Sporting's Jovane Cabral, but he was brilliantly denied from point-blank range by Dons captain Lewis, who bounced back after a poor mistake in Sunday's 3-0 loss to Motherwell.

McInnes' men were increasingly on the back foot after the break and Tomas squandered a great chance to put the tie to bed when he headed over a cross from Manchester City loanee Pedro Porro.

Tomas had got in between Tommie Hoban and Taylor, but nodded off target with 56 minutes on the clock at an empty Estadio Jose Alvalade.

Hayes latched on to a loose pass six minutes later and blazed over from a promising position when he had options inside the area.

It boosted Aberdeen, who had won six games in a row before last weekend's home defeat, and forward Scott Wright was introduced with 21 minutes remaining as they searched for an equaliser.

The lively Ryan Hedges had a right-footed shot deflected wide in the 80th minute to deny him a fifth goal in the Europa League this season before strikers Connor McLennan and Ryan Edmondson – the latter on loan from Leeds – were thrown on by McInnes.

Aberdeen were desperate for one final opportunity and it arrived with three minutes to go, but Hedges sliced a half-volley wide on the edge of the area and they again fail to make the group stage despite an encouraging display.