Written in Spanish, the message read: "Mejorate Pronto Alfredo" - "Get well soon Alfredo"
The Colombian striker was the subject of a controversial interview conducted by Sky Sports, in which his answers were mistranslated.
Morelos gave the interview in Spanish with the broadcaster providing English subtitles but at one point, the translation claimed the 23-year-old had accused Celtic fans of racially abusing him during an Old Firm game.
The Hoops lodged an official complaint with Sky Sports saying: "Translations provided to Celtic Football Club have shown inconsistencies between the words spoken during the interview broadcast and the subtitles used by Sky Sports. Celtic FC has asked Sky Sports to clarify their position on this matter."
Rangers fans attending a league match at Hamilton Accies in February last year held up a similar banner aimed at former Kilmarnock manager Steve Clarke after he claimed he had been subjected to sectarian abuse from home fans during a Scottish Cup match at Ibrox.