Trincao has been criticised by some after his 31 million euro move from Braga last summer, but Koeman has emphasised patience with the winger.
"He's come all the way from Braga, he's young," he stated.
"Taking a step to a club like Barcelona is a giant step. You don't have to go too fast.
"He is working very well, trying to earn minutes. He's not playing much, there's a lot of competition. We count on him a lot for the future of this club."
There are some inside Barcelona, including Koeman, that are pushing for the arrival of Manchester City defender Eric Garcia this January, despite the club's dire financial state. He does, however, recognise the difficulty in doing so.
"I have always said that I am not the one who has to [consider] the economic decisions of a transfer," Koeman explained.
"If the club thinks that it is not possible, it is not possible and we go ahead with what we have."