Sunderland have a number of promising young players in Tony Mowbray's squad who are pushing to become regulars in the side this season.

Daniel Neil has established himself as a starter, with 14 starts in the Championship, and the likes of Abdoullah Ba, Edouard Michut, and Amad Diallo should be hoping to follow in his footsteps.

The Black Cats have enjoyed success with young players over the years, whether that has been with signings or players from the academy, but they have also had their fair share of gaffes, in gems not fulfilling their potential or leaving too early.

One player the club had a nightmare with was young forward Sam Greenwood. The attacker left the club in the summer of 2018 and is now starting to make his breakthrough at first-team level.

He joined Arsenal as the Black Cats negotiated an upfront fee of £500k - with add-ons taking it over £1m - to sell him ahead of the 2018/19 campaign, with Stewart Donald unable to convince the gem to stay after 12 goal contributions in 15 games for the U18s.

Greenwood then moved to Leeds for a fee rising to £3m in the summer of 2020 and he was promoted to the first-team squad at Elland Road in January of this year.

Former Leeds striker Noel Whelan previously hailed the young forward's set-piece quality and described his deadball ability as a "weapon".

Jesse Marsch has also heaped praise on the gem in the past, saying: "First of all, he has a lot of flexibility to his game. He's played six, eight, 10, he can play striker. In some ways, it's not fair to him to try different positions, but he's an intelligent player. He fits within what we're trying to build within our team.

"He's a hard worker, he's an intelligent guy, he's able and that's the reason why we use him in a lot of positions because he's very adaptable. He understands tactics and his role and he has big talent."

Greenwood scored 21 goals and provided six assists in 40 U21 matches for Leeds and that was enough to convince the American head coach to promote him to the first team, where he has made 17 appearances to date - assisting two goals in the Premier League.

The 20-year-old has played four matches in the English top-flight this season and is showing that he is a player with the potential to become a regular at that level in the future, as he is being trusted with minutes at such a young age.

Therefore, former Black Cats owner Donald had a howler by failing to convince Greenwood to stay as they missed out on having a terrific young talent in the Academy of Light and were compensated with just £500k - as the add-ons were not likely to have been met due to him moving on to Leeds.

Sunderland supporters will now have to watch the rest of his career unfold and, if he continues to be a success in the top flight, wonder what could have been...