Is the fasting of one who has recently embraced Islam, without prayer, due to concealing his conversion from his family, ineffective or futile?

One who has recently embraced Islam is not permitted to abandon prayer under the pretext of concealing his conversion or fearing his family's anger. Rather, he is obligated to perform the prayer secretly if he fears harm. As for his fasting, according to the view that considers one who abandons prayer an apostate, his fast is invalid. However, if it is said that he is not an apostate, then his fast is valid, provided it is free from anything that would invalidate it.