When asked a few days ago on progress in the transfer market, Sunderland manager Alex Neil's response was pretty significant and could be read into in a few different ways.

“I can’t knock on the door anymore - there’s probably no door there anymore because I’ve pretty much bust it down,” the Scotsman said in regards to his discussions with the Black Cats hierarchy when it comes to new recruits at the Stadium of Light.

It seemed like somewhat of a frustrated response by Neil, who has seen four new players arrive at the club this summer - that includes wide player Jack Clarke who turned his loan spell from Tottenham Hotspur into a permanent move.

One of the eye-catching deals that Neil was able to get over the line was the signing of Arsenal's Northern Ireland international centre-back Dan Ballard, who was a man in-demand but the size of Sunderland was able to convince him to join the Wearsiders.

Unfortunately though, the 22-year-old will be spending some time on the sidelines, having suffered a fractured foot in just his third appearance for the club.

If Sunderland didn't need a new central defender before then, they definitely do now, and it may mean dipping into the loan market and looking at options in the Premier League - something that they have only done once so far this summer with Ellis Simms arriving from Everton and is already impressing.

Whilst there isn't many centre-backs in Premier League development squads that have much Championship experience, one individual who does is Teden Mengi.

The Manchester United man spent the second half of last season with Birmingham City, and the second half of the previous campaign with Derby County.

Mengi featured nine times under Wayne Rooney at the Rams, and at the Blues he also featured nine times, but that was restricted due to two injuries - both of which came to his hamstring.

A defender who is prone to picking up muscle injuries - not exactly what Sunderland need right now you'd think due to the Ballard situation - but if he's kept fully-fit, then Mengi could be an asset for Neil.

We know that Mengi is highly thought-of at Old Trafford as he was the under-23's captain whenever he played last season, as well as in the UEFA Youth League.

And with WhoScored detailing that Mengi's strongest asset is his tackling, as well as being able to comfortably play the ball out from the back, then he's exactly what the Black Cats need.

The 20-year-old is not short of pace either, although due to his hamstring problems, the youngster may be a bit more reserved in his attempts to use it going forward.

The need for a centre-back on Wearside though is desperate, and Mengi can perhaps help fill that void until Ballard is back - and then he could play in the same back-line as him.