Galbraith has only played senior football three times, twice for Northern Ireland and once as a Europa League substitute. He has, however, scored at the Keepmoat Stadium, playing for Manchester United' s under-21s against Doncaster Rovers in the 2019-20 Football League Trophy.
He joined on a season-long on Friday and with Arsenal loanee Matt Smith suffering from Covid and AJ Greaves suspended after his League Cup red card, Galbraith could even make his debut in Saturday's South Yorkshire derby at Sheffield Wednesday.
"He's a top footballer," said manager Wellens. "He's played (under-)23s football for a number of years and he needs that opportunity to prove he can step up and do it in a men's environment.
"Ability-wise he's right up there. He has a real chance of being a top player but he needs at some stage to take the plunge and prove he can handle the physicality.
"I've watched him a lot over the years and over the last two or three months it feels like his body's developing into a man's now.
"I think he's a Doncaster Rovers-type player and hopefully we can be a big part in his development.
"He's definitely going to have a good career. Whether that's at Manchester United, we all know the difficulties that can have.
"I believe over the next 10, 15 years he's going to be a really good player."
As a former product of the Manchester United academy, Wellens is well aware of the talent there and has shown a willingness to tap into it. Summer signing Aidan Barlow was released by the Red Devils in the summer of 2020, and Ro-Shaun Williams has also come from there, via Shrewsbury Town.
Part of the challenge for young players sent on loan can be to fend for themselves, but interestingly Wellens wants to see Galbraith keep his home comforts.
"We want him to ideally stay at home so he's concentrating on his football," he explained. "Sometimes the first loan is tough for young players but he's a Northern Ireland international, he's been at training camps and spent the whole of pre-season with the first team at United so we hope his experience of first-team dressing rooms helps him.
"People will be asking can he deal with the physical side? Give him an opportunity.
"We hope he enjoys his football, plays with a freedom and shows what a top talent he is but more than anything he influences our first team and we get the rewards from that.
"Ideally we'd have liked to have got a winger or a striker in first but the opportunity's arisen and we thank Manchester United for helping us out with a deal. Sometimes when really good footballers come along, you just take the opportunity.
"We were interested in early pre-season but at that time we couldn't do it."
Left-back Tommy Rowe is an injury doubt for Saturday with an Achilles problem.