The German is largely unknown in England, so who is he and what would he bring to South Yorkshire?
Blessin, 47, was a forward in his playing days, representing a host of German clubs including Lokomotive Leipzig, SSV Reutlingen 05 and Stuttgarter Kickers.
He later moved into coaching with the excellently-named Norbert Stippel, joining RB Leipzig's set-up in 2012 before being appointed as KV Oostende boss last summer.
Oostende finished second-bottom of the Belgian Pro League last season but have been transformed under Blessin, currently sitting fourth in the table and above giants Anderlecht on goal difference.
Good pedigree, then?
It certainly seems so. Leipzig have become known for their brand of football since being transformed by Red Bull's investment and Blessin has fully embraced the art of gegenpressing made famous by Jurgen Klopp's Borussia Dortmund.
“Honestly, a lot of jaws dropped after the very first session… We literally just ran for the first week!" said Oostende's Jelle Bataille.
"It has to be said that it paid off. We integrate the Gegenpress. He [Blessin] spoke about it from the first training session.
"We immediately understood that something was going to change. Had to change. We are physically much stronger than last season."
Blessin utilises the help of Alfred Ntiamoah, a former American footballer who goes by the nickname 'The Lion', as his strength and conditioning coach, whipping his players into shape to be able to cope with the demands of his pressing football game.
Curiously, KV Oostende are controlled by the same majority shareholder, Pacific Media Group, as Barnsley.
What's the attraction for United?
It's said that United were impressed by Oostende's performances this season. Prince Abdullah's United World owns Beerschot - who beat Oostende on the opening day of the Belgian season - and United board member Jan Van Winckel keeps a close eye on goings-on in his home country.
The Prince has also reportedly been impressed by Blessin's work with young players and ability to operate on a budget, as United look to cut their cloth accordingly when their impending relegation to the Championship is confirmed.
In the post-Chris Wilder era, United want to pursue a more international approach to recruitment in the future and and Blessin seems to fit the mould of head coach that they are looking for.
Blessin's Oostende squad is composed of players from 11 different countries, including Scotland and Northern Ireland, and the Blades hierarchy are keen to begin making more use of the United World project which includes Beerschot, Kerala United, Chateauroux, Al-Hilal United and United themselves.
"Whether we win or lose, Blessin quickly identifies our weaknesses," Bataille added.
"He will then devote the week of training to remedy them. Each week has its theme. It is the strength of our coach, he pushes us...to be better than the previous week."