The midfielder is due to leave the Catalan club at the end of the season and the Segunda Division outfit are one of several teams to wish him well on social media.
Numancia's Twitter account posted a photo of Iniesta from early in his career, along with the caption: "We have enjoyed much with you, Andres Iniesta. Thank you for always being an exemplary player and person for our youth."
However, eagle-eyed users on the social network spotted that the player's private parts were visible in the photo, through a gap in his shorts, reports The Sun.
Numancia have since issued a lighthearted apology on Twitter, saying: "We apologise Andres Iniesta. It was not our intention. And now that we have realised you are all so great at finding Wally, we want to admire your courage. There are few who equal you."
Iniesta has been tipped to join the Chinese Super League when he leaves Barca at the end of the season.