The forward was not selected in United’s squad after he missed the club’s Friday training session with “illness”.
Rashford’s absence from training came after he was spotted in a Belfast nightclub on Thursday night.
He then flew back to Manchester on Friday morning.
United were aware of Rashford’s trip to Belfast and gave permission to him to travel to Northern Ireland‘s capital on Wednesday.
The England star was visiting his friend and former academy team-mate Ro-Shaun Williams, who plays for Larne FC.
When asked about Rashford’s absence from United’s FA Cup squad by the BBC, a terse Erik ten Hag simply repeated that his decision was an “internal matter.”
He went on to say he will “Deal with it.”
In response to Ten Hag’s interview, Shearer said: “If it’s an internal matter, you’d think something is up.
“There’s a huge talent in there with Marcus Rashford. We’ve seen him be disciplined last season when he was late to a meeting before a game but something is clearly wrong – either at home or in his relationship with the football club.
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“He can’t keep doing this, he can’t keep wasting his talent because it’s not right.
“He needs strong management, someone to get hold of him and tell him there’ll be huge regrets come the end of his career if he continues doing this.
“You can’t keep doing it, it needs sorting now. Thirty goals last season, four this season. When I see him play, it looks like he’s got the world on his shoulders so it needs sorting now because he can’t really deal with it.”
It is not the first time ten Hag has fallen out with Rashford this season.
The manager slammed Rashford’s night out after his side were beaten 3-0 by Manchester City in a derby – making it clear there was a time and a place for his squad to party.
The Dutch boss said at the time: “I spoke with him about it. It’s unacceptable. He apologised and that is it.
“For us it’s an internal matter. He’s very motivated to put things right. He’s totally with us.
“He has made a mistake but that doesn’t say he’s not fitting in. I see him every day in training, what he’s doing, I know.”
Rashford was also dropped from United‘s visit to Wolves last season after he overslept and missed a team meeting.
The forward came off the bench that time to score the only goal of the game – but did not have the opportunity to replicate that today after being left out of the squad entirely.
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