The sides will meet at San Siro in the last 16 of the competition as Diego Simeone's men seek to continue their unbeaten run in Europe this season.
However, they face a Milan side who have found fresh impetus under new coach Clarence Seedorf and Gabi feels that reputation and past form will count for little on Wednesday.
"Right now, at this stage of the Champions League, the favourites are decided on the field," he said.
"We respect Milan, a team with great players. We are thrilled to play this game at this stage."
While Milan sit ninth in Serie A after an inconsistent campaign to date, Atletico remain firmly in the hunt for the Liga title - sitting third, level on points with Barcelona and Real Madrid.
Despite suffering three defeats in a row in all competitions earlier this month, Gabi is confident that Atletico are on course for a successful season and called for his team-mates to gain a positive first-leg result.
"We have won the right to play this game and come to play with high hopes, looking for a good result, making a great game and following the line we are on," he continued.
"We want to do our work as we (did) before and get a good result for the return at the Vicente Calderon."
‘The pure simplicity of the way Slot has managed the squad is probably the biggest thing I could say about him. It’s not broken, so let’s get on with it’: Liverpool legend full of admiration for Jurgen Klopp's successor at Anfield
‘I trained at Spurs and thought they’d give me a chance. But I received a letter thanking me but saying they didn’t think I was good enough – I was gutted’: How Tottenham missed out on signing Wales legend John Toshack
