Sunderland transfer news: Kristjaan Speakman explains why Aiden O'Brien has been allowed to leave

The 28-year-old’s contract at the Stadium of Light was set to expire at the end of the season, while he has fallen down the pecking order following the arrivals of Jack Clarke and Patrick Roberts on Wearside.

O’Brien was set to join Doncaster in the summer, yet the deal wasn’t completed in time.

The forward has made 17 League One appearances for Sunderland this season, while he also bagged a hat-trick at Blackpool in the Carabao Cup.

Sunderland’s Sporting Director Kristjaan Speakman said: “Aiden’s contract was due to expire this summer and although he has had impactful moments throughout the season, he has consistently voiced his desire to play regular football.

"We feel this move gives him the best opportunity to secure more playing time whilst also supporting his career in the long-term and we wish him well for the future.”

O’Brien has signed for Portsmouth until the end of the season, with Pompey boss Danny Cowley highlighting the player's versatility.

“We’re really pleased to sign Aiden and from the moment I spoke to him, there was an energy and enthusiasm to join us,” said Cowley

“We’re lucky to be at such a renowned football club because there are so many players who want to come here.

“Aiden brings us many different qualities and can play across the forward line, making penetrative runs.

“He looks after the ball well and links the play, while he can also drive forward and is always a goal threat.

“We’re really looking forward to him being part of this group and he knows quite a few of the lads already, which is important when you arrive on a short-term contract.”

Sunderland are also looking to make more signings before tonight’s 11pm deadline.

The Black Cats look set to beat Ipswich Town to the signing of Fleetwood midfielder Jay Matete, while they have also been credited with interest in Fulham centre-back Terence Kongolo.

Kongolo, 27, hasn’t featured in the Championship for the Cottagers this season.