It's no secret that Tom Cruise is a notable Scientologist, but a few revelations in the HBO documentary “Going Clear,” which premiered Sunday, must be hard for fans to stomach. Allegations that the actor allowed his children to be turned against his former wife Nicole Kidman, had the actress' phone tapped and has ignored myriad potential abuses by the Church of Scientology -- while accepting lavish gifts and honors -- are sure to have many taking a darker view of the star. With the fifth "Mission: Impossible" movie coming this summer, how will the fallout from "Going Clear" affect Cruise's box-office appeal?

For years, Tom Cruise has been a public face of Scientology, championing the religion with his time and money and defending it in interviews. At the same time, he has shied away from addressing alleged abuses of the church – especially those surrounding his friend and church president David Miscavige – and speaking about his experience within the Scientology community. University of Southern California professor and celebrity brand expert Jeetendr Sehdev says that is a big problem.

“People question why an ambassador [of Scientology] comes forward in some circumstances, but not in others,” Sehdev told International Business Times Tuesday. “What is necessary is for Tom Cruise to provide context for his involvement.”

Indeed, the public seems to fault Cruise, not for his beliefs, but for not explaining his involvement and not acknowledging, let alone attempting to stop, the abuses that seem to plague certain areas of the church’s administration.

In the tweets below, "Going Clear" viewers admonish Cruise for not speaking up:

However, that acknowledgment may never come. The Church of Scientology is known for its veil of secrecy. “Going Clear” details alleged blackmail files the church maintains for certain figures -- including John Travolta -- to prevent them from speaking out against it. That's bad news for Cruise.

“[The Church of Scientology] is seen as a highly secretive institution and [the public] does not respond well to celebrities being highly secretive,” said Sehdev.

Sehdev explained that before social media Cruise would have “had control over the conversation” about his involvement with Scientology. However, now the conversation is happening with or without him and the actor’s attempts to brush controversy under the rug largely have failed to silence critics.

“It will absolutely have a box-office effect and an effect on his appeal,” said Sehdev.

Cruise, once arguably Hollywood’s most bankable name, stars in “Mission: Impossible – Rogue Nation,” set to premiere on July 31. The previous “Mission: Impossible” movie, 2011’s “Ghost Protocol,” was a box-office success, but the star has not had a major hit since -- striking out with “Edge of Tomorrow,” “Oblivion,” “Jack Reacher” and “Rock of Ages,” despite decent reviews.

If “Rogue Nation” fails to perform, the pressure will be on Cruise to do something to halt the decline in his marketability. In the end, he may have to choose between Scientology and his career.