The 32-year-old Scotland captain, who confirmed his departure from Liverpool in April after losing his starting place to Milos Kerkez, was an unused substitute at Villa Park on Friday as Aston Villa's 4-2 win dropped the Reds to fifth place and left Champions League qualification unresolved heading into the final day.
Robertson posted on Instagram immediately after the final whistle.
"A performance which sums up our season. A long way short of the levels of this club and what you rightly expect of us."
"But I can only thank you for the last nine years of travelling up and down the country and all over the world packing out away ends wherever we go. Will see you next week for one last time."
The defeat was Liverpool's 12th in the Premier League this season, equalling their worst total in 11 years. They have now lost 20 matches across all competitions in 2025-26, a record for a Arne Slot squad that won the title in his debut campaign.
Robertson joined Liverpool from Hull City for just £8 million in 2017 and won every major honour available under Jürgen Klopp — the Champions League, Premier League, FA Cup, League Cup and Club World Cup. He made 31 appearances this season but only 15 starts as Kerkez, 10 years his junior, cemented the left-back role.
His farewell at Anfield against Brentford on the final day is now laden with pressure rather than the pure celebration it might have been. Liverpool need to win and are relying on results elsewhere to secure a top-five finish. Robertson will want to end his Liverpool career with Champions League football secured — whether or not he plays a part in making it happen.