The Celtic centre-back made 31 appearances in the Scottish Premiership this season, but was unable to help his side achieve a tenth straight league title as the Hoops finished the campaign in second place, 25 points behind winners Rangers.
Ajer has already revealed that he expects a move away from Celtic after spending five years with the Hoops and Newcastle have been credited with being willing to snare him away from Scotland.
And the Magpies have done their homework on the 23-year-old centre-back as they have monitored his progress extensively.
Magpies manager Steve Bruce wants to reinforce his defence and is looking to land at least one central defender.
The Norwegian stopper has won three Scottish league titles, three Scottish Cups and three Scottish League Cups in his time at Celtic since joining the Hoops.
Newcastle could be able to sign Ajer for a smaller fee than would have been the case last summer as he is into the final year of his contract.
Celtic may be forced to sell Ajer in the upcoming transfer window to avoid losing him for free next summer.
It remains to be seen whether the towering centre-back will make a move to St James’ Park with Newcastle looking to bolster their options in defence.