Zinckernagel spent the previous season on loan with Nottingham Forest and helped their promotion charge.
The winger made 45 appearances in the league and contributed with six goals and seven assists, playing nearly 75 minutes of the playoff final.
Zinckernagel would be in for a season in the Championship with Watford, but for Olympiacos who are keen on the winger.
Olympiacos inch closer to his signing as the winger will travel to Greece in the coming 24 hours for a medical, according to Greek daily Sportime.
The Greek champions have a personal agreement with the winger and, with the medical scheduled in a short amount of time, things are moving in the right direction for the transfer to take place.
Zinckernagel spent only half a season playing for Watford after transferring to Vicarage Road in January of last year as he spent the previous campaign at the City Ground.
His contract with the Hornets runs until the summer of 2026 but he is set to depart Vicarage Road much earlier than that.
