Former Sunderland winger Johnston has not figured in Boro's first team for well over a year and has just completed a successful loan spell at Sheffield Wednesday. The Scotsman's career has stalled since his move away from the Stadium of Light, he has failed to hold down a regular place at either Rangers or Boro.
Vidmar, 34, will complete his one year contract at the Riverside in the summer and with new signing Chris Riggott jumping ahead in the queue to provide cover for Gareth Southgate and Ugo Ehiogu, the Australian is unlikely to be offered a new deal by Steve McClaren.
With Sunderland in dire financial straits after a disastrous season, they will be searching for cut price replacements for high earning "stars" next season. Kevin Phillips will lead an exodus of players from Wearside in the summer with Boro still being linked with the former England frontman.