Having been at Millwall his entire career, Aiden O'Brien finally departed The Den for the Sunderland last summer.

O'Brien had enjoyed six seasons in the Lions' first-team, but his opportunities decreased under Gary Rowett which finally led to him moving away from South London.

So have things gone for the Republic of Ireland international since moving to the Stadium of Light? What issues does he face in the North East? And what could be next for the attacker?

Here, we take a look.

How's it gone so far?

It's fair to say that O'Brien's time with the Black Cats is gathering pace.

Until the New Year, his only goal in Sunderland colours came in their thumping EFL Trophy win over Aston Villa Under-23s back in September, although he's since added to his tally.

O'Brien has started 11 games in League One this season, appearing 22 times in all competitions - with other goals coming once again in the EFL Trophy against Port Vale before finally striking in the league against Plymouth last month.

After biding his time for the majority of the campaign, O'Brien has now started all of Sunderland's previous eight matches.

What issues does he face?

O'Brien has previously spoken about wanting to play through the middle rather than out wide, and although that would appear difficult with Charlie Wyke in excellent form, the recent departure of Will Grigg should pave the way for the former Lions man for further chances as a striker.

However, Lee Johnson has been persistent on playing one up front, so O'Brien will have to remain patient, although following a tricky opening few months with the Black Cats, he'll be more than happy to be in the starting XI, regardless of where that might be.

But at present, O'Brien has the shirt, so it's down to him to ensure he keeps it.

What's next?

Despite dropping more points at MK Dons on Saturday, following the victory at Stadium MK earlier this week, O'Brien's Sunderland are just 90 minutes away from a trip to Wembley in the EFL Trophy, whilst their promotion charge is starting to gather pace.

O'Brien would've made the switch to the Stadium of Light with aspirations about making a swift return to the Championship.

Sunderland are currently sitting 8th in the League One standings, but having played fewer than some of the sides around them, O'Brien will be hoping his wish becomes a reality in the coming months.