The England international was not involved in Man United's FA Cup fourth-round contest with Newport County on Sunday afternoon due to illness.
Rashford did not report for training on Friday, with Ten Hag saying during his pre-match press conference that the forward was a major doubt for the FA Cup fixture due to an illness.
It then emerged that Rashford had been out in Belfast earlier in the week, with the forward photographed on Thursday evening in a nightclub, before allegedly returning to Manchester on Friday morning.
There have been suggestions that the 26-year-old could face disciplinary action, and it remains to be seen whether he is involved in Thursday's Premier League clash with Wolverhampton Wanderers.
Ten Hag has called the issue «an internal matter» and insisted that he will «deal with it», but the ramifications for Rashford at this stage are unclear.
«So he reported ill, for the rest it's an internal matter, I deal with it. As I said, it's an internal matter,» Ten Hag told reporters during his post-match press conference.
«For you (it raises more questions than answers), but not for me. It's an internal matter, I will deal with it.»
When pressed again on the matter and asked whether it was a demonstration of the «no-good culture» at the club, he responded: «I don't go in this case, I've talked before about it. I think we played a good game and now we move on. We will deal with it, I will deal with it.»
In his absence, Man United booked their spot in the fifth round of the FA Cup courtesy of a 4-2 success over Newport County, with Bruno Fernandes, Kobbie Mainoo, Antony and Rasmus
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