Rangers manager Stuart McCall said he sympathises with Newcastle loanee Gael Bigirimana, but believes he should never have been signed by the club.
Midfielder Bigirimana has yet to feature since signing in January after being diagnosed with a mystery illness.
He was brought in by former chief executive Derek Llambias without being given a medical.
"It's an unfortunate circumstance that really should never have happened," said McCall.
The Burundi-born England youth cap signed alongside four other Newcastle players before the end of the transfer window, but so far only Haris Vuckic has been a regular in the team.
Remie Streete was injured on his debut, Northern Ireland winger Shane Ferguson has been ruled out for the rest of the season and Swiss defender Kevin Mbabu has only featured for Rangers' youth side.
"Bigi has got a medical condition which is a personal matter," said McCall. "The doctor and consultant are all involved in that.
"I knew him at Coventry. I remember watching him and thought when I came into the job he will be a good one to bring in and give us a bit of energy.
"Unfortunately because of his medical condition he won't be able to play for us. But that is as big a blow to the kid as it is for us. It's not his fault, this has been nothing to do with him.
"He comes in with a smile on his face each morning, he trains with the fitness coach as hard as he possibly can.
"So as disappointed as we are that we can't use him, you have to think of the boy in this matter because he can't go back, he can't play for anyone else."
Bigirimana, 21, has made 28 appearances for Newcastle since arriving from Coventry City in the summer of 2012 for £1m.
But he has not played for the Magpies' first team since August 2013.
McCall added: "Should these guys ever have been sent here? Well, with Bigi being unable to play that's a no-brainer. With Shane, he was on his way back but had a little setback.
"But I think if you look at it in all honesty, anybody who comes up for a six-month loan should have a medical - obviously that is not the case.
"If that had occurred, two or three of the loans may not have happened.
"But, none of the players are at fault here. Shane has not been up but the rest come in and train as hard as they can. They are doing their utmost to be involved."