Middlesbrough defender Aden Flint joined Cardiff City last week, for a reported fee of around £4million plus add-ons, after just one season at the Riverside Stadium.

The 30-year-old joined Middlesbrough from Bristol City on a four-year deal last summer and was a key player last season, making 39 appearances in the Championship as Tony Pulis' side just missed out on the play-offs.

Jonathan Woodgate now faces the difficult task of replacing the centre-back before the end of the transfer window.

In our latest FLW Six Pointer, we look into Flint's departure from the Riverside Stadium in more detail and discuss how Middlesbrough will replace him.

First of all, why exactly did Middlesbrough let Flint go after just one season?

"Flint arrived at Middlesbrough from Bristol City a year ago as one of the most highly-rated centre-backs in the Championship.

"However, it's the start of a new era at the Riverside Stadium and Woodgate will have his own ideas about where he wants to take the club.

"It seems as though Woodgate is keen to play possession-based football, which will involve lots of passing and movement.

"Flint is solid defender at Championship level, but it's clear from his performances for Middlesbrough last season and in their recent pre-season friendlies that he isn't comfortable with playing out from the back.

"He was a fantastic signing for Pulis, but it seems as though Woodgate is not convinced that the defender can adapt to his style of football."

Is Flint a good signing for Cardiff?

"Flint is a top defender at Championship level and I think he could turn out to be a fantastic signing for Cardiff.

"He's a tough-tackling, no-nonsense defender and a real leader on the pitch

"On top of that, he is a big physical presence and his height and aerial prowess make him a real threat from-set pieces.

"He may not have been the right fit for Woodgate's style of football, but I think he will be perfect for Neil Warnock and he could form a formidable partnership alongside Sol Bamba at centre-back."

Do you think Middlesbrough will regret letting him go?

"I think that's something that will become clear in time. It depends on whether Middlesbrough can find a good replacement for him and how well he does for Cardiff.

"Flint is a great defender and I was impressed with his defensive contribution last season, but I'm not convinced by his ability to play out from the back, which seems to be the style of football Woodgate wants the team to adopt.

"It could end up being a sensible decision for Middlesbrough to let Flint go, but I do think they may come to regret selling him to a potential promotion rival."

Is the reported £4million plus add-ons for Flint a good deal for Middlesbrough?

"I don't think so, not given the circumstances.

"Flint had three years remaining on his contract at the Riverside Stadium, so I'm surprised Middlesbrough didn't hold out for a bigger fee for the centre-back.

"He joined Middlesbrough a year go for a reported fee of around £7million, so it doesn't seem as if Boro have made any sort of profit on him and that has to be considered bad business.

"Not to mention that he's one of the best defenders in the Championship and that they have sold him to a potential promotion rival for the coming season."

Where does Flint's departure leave Middlesbrough?

"Flint may not have fitted into Woodgate's new-look side, but his departure does leave Middlesbrough worryingly short at the back.

"With Woodgate likely to play a back four next season, there's a good chance that Daniel Ayala and Dael Fry could form a good partnership at centre-back.

"Boro's other centre-back options include Ryan Shotton, who isn't that comfortable playing out from the back, and George Friend, who is recovering from an injury setback.

"With just a few weeks to go until the start of the new season, Woodgate will have no choice but to dip into the transfer market to bolster his defensive options, whether that means signing someone on loan or on a permanent deal."

Who could Middlesbrough sign to replace Flint?

"I personally think somebody like Fikayo Tomori would be an ideal replacement for Flint, although it remains to be seen whether Frank Lampard is prepared to send him out on loan from Chelsea again.

"Somebody like Pontus Jansson would have been ideal given his ability to play out from the back, but he obviously isn't available having just signed for Brentford.

"I'm not sure Woodgate would have been prepared to sell Flint unless he already had a potential replacement in mind, but he really hasn't left himself with a lot of time to get a deal sorted before the end of the transfer window.

"It will be interesting to see who he decides to turn to, as there doesn't appear to be too many obvious choices at the moment."