The centre-back has departed Rotherham following their relegation from the Championship and is seemingly weighing up his options ahead of next season.
The Daily Record reports that Danny Cowley's made contact with Robertson ahead of a potential move to Fratton Park, while Aberdeen are also keen.
However, the ex-Blackpool man now supposedly has interest from overseas.
According to reports, Robertson has held talks with Hapoel Jerusalem via Zoom and is now waiting for an offer in writing.
The Israeli club have just won promotion to the top flight and want Robertson for the upcoming campaign.
Pompey will be in the market for a centre-back this summer, with only Paul Downing and Sean Raggett under contract.
Meanwhile, Rasmus Nicolaisen's loan spell from FC Midtjylland has come to a close.