Lucas Paquetá had a lacklustre performance during his highly-anticipated return to Flamengo in a 2-0 defeat to Corinthians in Sunday's Brazilian Supercup.
Paquetá, who rejoined his boyhood club last week from West Ham, came on in the second half.
With Flamengo trailing 1-0 and playing with 10 men after Jorge Carrascal was sent off, Paquetá missed a golden chance to equalise when he struck over the bar from the six-yard box, much to his surprise.
"I'm sad," Paquetá said.
"I was eager to score. Honestly, I can't miss a goal like that, there's no excuse, I have to score.
"I chose a move that wasn't the best and ended up making a mistake. I'll work hard so that next time I can put the ball in the net."
Flamengo signed the Brazilian midfielder ahead of Sunday's Supercup after weeks of negotiations with West Ham.
With a record €42.25 million ($50.15m) transfer fee agreed, Paquetá is the most expensive player ever signed by a club in North and South America.
However, he struggled under the pressure of his first game for Flamengo since 2018 and only completed five of his 10 passes as his team missed out on the first title of the season.
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"I know the responsibility that comes with the investment that Flamengo has made," Paquetá said. "But that's not a burden for me because I'm at home."
Paquetá had wanted to return to Brazil ahead of the World Cup and was thrilled to be back playing for Flamengo.
"It was special, without a doubt," he said of Sunday's game. "I waited a long time for this moment, to be here wearing this shirt.
"Unfortunately, it didn't go the way I would have liked, but it's gratifying to be back home. I'm going to work hard, give my best, and I'm sure we'll win a title this year."
