"is only mentioned" is correct and usable in written English.
You can use it when you want to emphasize that something is mentioned, but not stated or explained in more detail. For example: "The importance of physical exercise is only mentioned in the essay, without any further discussion."
Supporting growth is only mentioned once.
The Enbridge spill is only mentioned briefly in addendums.
Defocus - this option is not recommended and is only mentioned for completeness.
But his 1989 suicide, which is only mentioned in the epilogue, seems to tell another story.
Mr. Gingrich is only mentioned once in Mr. Cannon's book, in a discussion about the post-Reagan era.
Smith offers a very optimistic vision: prejudice exists, but tolerance appears in equal measure, and racist violence is only mentioned briefly and at second hand.
The ending can't be spoiled because no one knows it — the resolution may hinge on a woman named Tina who is only mentioned in passing.
The 'business side' of the organization is only mentioned briefly in analyst conference calls and the conversation is not conducted with the same team that faces the public.
In histories of early Chinese cinema, Pu Shunqing is only mentioned in passing as China's first female scriptwriter for Cupid's Puppets (1925), a Great Wall Film Company film co-directed by her husband, Hou Yao, and Mei Xuechou.
Curiously, in the never-ending stream of material published on the financial crisis, the role that tax havens played in mediating the deep fault lines of the global economy is only mentioned, if at all, as a footnote.
Despite the temptation to include songs where blood is only mentioned in a line or a brief refrain, I have tried to choose music that is actually about blood or where the lyrics are saturated with it.
