The Reds defender missed his side's recent 5-0 victory over Gibraltar in the European qualifiers.
According to Greek football outlet Hellas Footy, manager Gus Poyet had been informed Tsimikas, along with teammates Petros Mantalos, Dimitrios Kourbelis and Manolis Siopis, were all ineligible to play.
However, all four players had each picked up two yellow cards, with rules stating a suspension only occurs after three.
The mistake was reportedly down to the Greek Hellenic Football Federation, who appear to have got their numbers mixed up.
Poyet's troops did run out comfortable winners in the end with Dimitros Pelkas opening the scoring on nine minutes.
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Konstantinos Mavropanos and Giorgios Masouras both netted twice in the route as their side went level on nine points with the Netherlands in Group B.
Tsimikas, meanwhile, is expected to agree fresh terms at Liverpool until 2027.
He has made 62 appearances in all competitions for the Reds since joining in an £11.75million deal from Olympiacos in 2020.
The left-back netted the winning penalty in the club's 2022 FA Cup final win over Chelsea.
According to The Athletic, a new deal is in the pipeline, despite Tsimikas playing just once this season.
His only appearance so far was during Liverpool's 3-1 win against Bournemouth in August when he came on in injury time.
As well as the 2022 FA Cup, the Greek has also got his hands on the League Cup, and a runners-up medal in the Champions League final that May.