Union have been preparing for Andersson’s departure for a while as interest has grown.
The Sweden international scored 12 goals and clocked up three assists in his first Bundesliga season.
Celtic will be the first team to make a move with a bid said to be imminent.
In addition to Celtic, French side Lille could also firm up their interest with a concrete bid.
Thanks to an opt-out clause included in his new contract this February, 29-year-old Andersson can leave for a ‘mid single-digit million’ transfer fee.
The exact amount depends on his destination – English clubs for example would have to pay 30 per cent more than German sides.
According to Kicker, the clause expires in August, meaning a decision on Andersson’s future will come in the next fortnight.
In Germany, Schalke have also been monitoring the player’s situation.
Andersson joined FC Union in 2018 on a free transfer from Kaiserslautern following their relegation.