Apologetic Yermin Mercedes in uniform for White Sox’ Triple-A team

Less than 24 hours after saying he was stepping away from baseball, Yermin Mercedes was in uniform for the Charlotte Knights, the White Sox’ Triple-A affiliate, for their game in Durham, North Carolina, on Thursday.

On his Instagram account Wednesday, Mercedes, who was demoted to Charlotte after falling into a prolonged slump, said he was quitting. On his Instagram Thursday, Mercedes declared, “I’m back.”

Sox manager Tony La Russa probably wasn’t surprised.

“Kind of understand,’’ La Russa said Wednesday after hearing the news. ‘‘You’re in Triple A, had a taste of the big leagues, and you can get emotional. I’ll reach out to him.

“It could be just a little frustration. I’ll explain to him that he has a big-league future.”

Apparently, it was just that. Mercedes apologized for his actions.

“I will never give up,” Mercedes posted. “I lasted 10 years in the minor leagues. My dream is to be a player established in the big leagues.

“I apologize.”

A defensively challenged catcher used as a designated hitter after making the major-league roster out of spring training, Mercedes, 28, got his chance to play because of Eloy Jimenez’s injury and took the major leagues by storm, going 8-for-8 to start the season and earning American League Rookie of the Month honors for April and national attention. The 5-11, 245-pounder enjoyed instant fame — he had a hamburger named after him by a local restaurant — but slumped terribly in the second half of May and in June and was optioned July 2.

In 15 games, Mercedes was batting .298/.365/.632 with four home runs at Charlotte and probably thought he would return to the Sox when catcher Yasmani Grandal went on the injured list two weeks ago. But the Sox called up light-hitting Seby Zavala because of his superior defensive and game-calling skills.

“You go to Triple A, it’s an adjustment,” La Russa said. “You’ve got to figure out a way to tough it out.”