The 27-year-old England international sat out a third straight game on Sunday as United slumped to a 3-0 home loss to Bournemouth.
Rashford was also omitted from the squad for the derby win at Manchester City earlier this month and Thursday's League Cup quarter-final defeat by Tottenham.
Two days before the Spurs loss, Rashford said in an interview that he was "ready for a new challenge and the next steps" of a career that began in the United academy.
"It is a hard situation but I understand that this kind of player have a lot of people around them, and making some choices that sometimes is not the first idea from the player," Amorim told Sky Sports on Monday.
"They chose to do that interview because it's not just Marcus. I understand that so for me as a coach I'm just focused on the performance, the way he trains.
"The rest, I think, is better for me and the club to deal with that when the times comes."
Amorim also expressed his support for Rashford, who is under contract until 2028, and is keen for the player to stay at United.
The Portuguese said he can "separate" his relationship with Rashford from the decisions of the people advising him.
"At the moment I'm just focused on improving Marcus," added Amorim.
"We need a lot in this moment, (from a) talented guy like Marcus, and I forget for now the interview. I just see what I see on the pitch."
United's defeat by Bournemouth left them 13th in the Premier League, their lowest position in the top flight at Christmas since 1986.
Amorim's side return to action at Wolves on Boxing Day before hosting Newcastle next Monday.
© 2024 AFP