The Colombian internationalist was shown a second yellow card and subsequent red for simulation in the dying moments of the December match, which ended in a 2-1 win for Steven Gerrard's side.
As he made his way off the pitch, he sparked controversy with a gesture aimed at the home supporters. But the 23-year-old claims he was reacting to racist abuse from fans.
The former HJK Helsinki striker has rarely spoken to the media since his arrival in Scotland, but opened up on his childhood in Cereté as well as his dsciplinary record in Scottish football in a rare one-to-one.
"Against Celtic, we were winning in added time. I fell down - whether it was simulation or not is up to the referee - but afterwards it was very frustrating to hear the crowd screaming at me," he told Sky Sports.
"[The fans] were saying offensive and racist words. I wasn't trying to instigate or incite anything [with my throat-slitting gesture], I just wanted them to stop.
"It was sort of a symbol, saying, 'Come on guys, the game is over. This doesn't need to continue. I understand why you're criticising me but now it's over.'
"I've experienced racism on and off the pitch. It's very sad, but it's not something that affects me much. I just try to focus on my job, which is scoring goals and winning matches."
Morelos has often been a target for opposition fans, and had a drink thrown at him during a league match at Motherwell as he celebrated a goal. He was also dismissed in that match for gesticulating at the fans - something that he admits was borne out of anger.
"Against Motherwell, we were winning a very important match; I scored a very important goal and I celebrated," Morelos recalled.
"I didn't mean to offend anyone. If you look back, I have done this celebration at home matches and away matches.
"Sometimes it's frustrating when a crowd is throwing coins or drinks at me, he added. "Obviously fans saying racist things, or chanting about my mother... it's very offensive.
"These things affect my family, and they are frustrating. But I am a strong person; I'm unfazed by it. It's more about my family and them feeling nervous about the situation.
"It won't drive me out - generally, I've felt safe and my goal is to stay focused on my game and on winning the title and trophies."