El Ghazi, who joined Mainz in September, had been suspended on October 17th over the post which he has since deleted.
"Anwar El Ghazi has been issued an official warning by 1. FSV Mainz 05 for a post that he published on social media two weeks ago," the club said.
"In this post, the Dutchman took a position on the conflict in the Middle East in a manner that wasn’t tolerable for the club," Mainz said in a statement.
The club, which did not provide further details about what El Ghazi had written in the deleted post, said the player had undertaken several talks with club officials and had distanced himself from the post.
"Given his commitment to upholding the club's values and the remorse shown by El Ghazi, and in keeping with the club's culture of using mistakes as an opportunity to learn, Mainz have opened the door for him to resume his duties," the club added.
"As such, Anwar El Ghazi will return to training and matchday-related activities with 1. FSV Mainz 05 soon."
Israel has said 1,400 people were killed when Hamas-led militants stormed through the south of the country on October 7th and took 229 hostage. Hamas has released four so far and said 50 have been killed in retaliatory strikes.
Medical authorities in Hamas-run Gaza, which has a population of 2.3 million people, said on Monday that 8,306 people - including 3,457 minors - had been killed.
Mainz, without a league win this season, are in last place in the Bundesliga with three points.
