THE Middlesbrough transfer rumour mill is in full flow with more teams announcing their retained lists. 

Sunderland announced the names of the players the intend to keep for next season as former Boro captain Grant Leadbitter was deemed surplus to requirements. 

The Black Cats say they've offered a deal to utility man Luke O'Nien who is yet to put pen-to-paper on a fresh deal at the club. 

According to Football Insider, Boro are said to be one of the clubs monitoring O'Nien's situation along with a number of other Championship sides.

Sunderland will be hopeful of O'Nien commiting his future to the Stadium of Light while the eyes of Boro's recruitment staff could light up at the thought of capturing the 26-year-old on a free transfer. 

He's made 140 appearances, scoring 11 goals, in three seasons on Wearside. 

Meanwhile, Boro are said to be 'admirers' of FC Midtjylland striker Sory Kaba.

According to the Daily Telegraph, Swanses City and Premier League-bound Watford have taken a look at the Guinea forward, while Neil Warnock's side are also said to be admirers.

The 26-year old has netted 14 goals in Denmark this season.

Goalkeeper Joe Lumley is Boro's only signing of the summer so far.

He'll link up with the team for pre-season once his contract at Queens Park Rangers expieres.