“We all kick the same ball,” he tweeted, expressing his frustration at the abuse posted online.
“I love this club. I love my city. This club has been my home from the age of 7.
He went on to admit he had encountered “physical obstacles” which had affected his performance as a player.
“I’d be the first to say I’ve struggled this season,” he wrote.
“It’s not about commitment, dedication or ability. The reality is, I’ve had physical obstacles I’ve had to overcome and that I’m still managing.
“That being said, there are no excuses for last night, we simply weren’t good enough.
“I’m really sorry that we couldn’t bring the silverware home.”
“We all wear the same shirt. We all kick the same ball.
“I’ve been playing this game from the day I could walk. I’m built for criticism of my performance but I can’t accept the ape, monkey, baboon, banana, jungle talk.
“As a United fan myself, it’s really difficult stuff to read. And I can only think about how this would have made me feel as a 7 year old reading it. How would I ever have any faith in humanity?”
On Thursday morning, Mr Rashford said he had received a torrent of racist abuse after the match.
“At least 70 racial slurs on my social accounts counted so far,” he wrote on Twitter.
“For those working to make me feel any worse than I already do, good luck trying.”
He later thanked the people who had reached out in support following his earlier tweet.
“To all of those that have been encouraging, to the staff at FA and United who have reached out, for these kind words and those I’ve read on here, thank you. Your support is never taken for granted.
“I’m 23. I still have a lot to learn and this disappointment will only add to my experience and growth.”