Speaking in the changing rooms at Kingsholm, Sinfield admitted there was plenty of work to be done in the defensive area.
"We need to be better ... it was always going to be tough, a battle and challenge tonight," he said.
"I just think our line speed and contact weren't where it needed to be tonight ... we need to improve that.
"Our effort was great but attitude was a bit off ... it's my job to fix that; I've got a bit to do."
Looking ahead to next weekend, Sinfield believes the challenge of the league's benchmark outfit Saracens is an exciting one.
"I think it's a great challenge for us at this time of the year, they are obviously a brilliant club," Sinfield said.
"But, we have got to improve."
Discussing his tenure so far at Tigers, he added: "It has been a brilliant challenge and the welcome I have had from everybody has been wonderful."