League One rivals Portsmouth favourites to sign ex-Sunderland target despite shock interest from Poland
Ekstraklasa side Slask Wroclaw have joined the race for the 27-year-old, who is out of contract this summer having rejected a new deal at Rotherham, report the PA agency.
The centre-back is involved in a transfer tussle between Wroclaw, Portsmouth Ipswich, Aberdeen and Hapoel Jerusalem.
The PA news agency understands Aberdeen have made a fresh approach, with boss Stephen Glass having made him a priority signing.
Aberdeen are in the Europa Conference League second qualifying round but a move to Poland would also offer Robertson European football next season, with Wroclaw having reached the first qualifying round by finishing fourth in the Ekstraklasa.
Israeli Premier League newcomers Hapoel Jerusalem have also made a contract offer, with other Israeli teams chasing Robertson.
Ipswich remain keen as Paul Cook looks to rebuild his squad at Portman Road, but Pompey are well placed after Robertson held positive talks with boss Danny Cowley.
Former Huddersfield manager Cowley is shaping a squad to return the club to the Sky Bet Championship having missed out on the League One play-offs this season.
A return to boyhood club Aberdeen, where Robertson started his career and made 68 appearances, does remain an option and the former Scotland Under-21 international has already visited the Dons’ training ground.
Robertson has been at Rotherham since 2018 after joining from Blackpool and helped them return to the Championship in 2019, although could not stop their relegation this season.
Back in 2018, Sunderland – under then boss Jack Ross – were keen on a move for the Scottish defender who turned down a new deal at League One rivals Blackpool.
The left-footed centre back was previously on Ross' radar when he was manager at St Mirren, and was lined-up to strengthen Sunderland's backline after the Scot took charge.
But despite looking to be frontrunners for his signature for a large spell, Sunderland were pipped to the signing by Championship side Rotherham United.
He is now set to be on the move again.