The 19-year-old is keen to be part of the Red Devils squad which travels to face Chelsea in the fourth round of the competition on Wednesday after playing in the 2-1 win over Newcastle United in the previous round.
Keane admitted the game against Alan Pardew’s side left him physically and mentally tired, and is aware that only further exposure will help him cope.
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"You play games with more pressure when you get to a higher level," he told MUTV. "Every game you play, you've got more experience of playing for points and playing because it means something rather than just friendlies.
“When you get called into the first team, you're used to being desperate to win and getting the three points [or getting through].
"I was so tired [after the Newcastle tie]. I've never been that tired after a game. Mentally as well as physically because of the concentration, how the day went building up to it and then the 90 minutes was tough but we did well.
"Obviously it was harder physically being on the big Old Trafford pitch but mentally playing against more experienced players means you have to be concentrating the whole time and not taking any breaks. It does take it out of you but, as long as you concentrate for 90 minutes, you're fine.
"Shola Ameobi has played in the Premier League for years so you know if you're playing against him, you're probably good enough to play in the Premier League. I see it as a challenge to yourself and the whole back four coped reasonably well."
United have had a number of defensive injuries already this season which has led to the England Under-19 international being involved in a couple of first-team squads.
Keane is eager to step up but wants to play off the back of his own merit, not just as a temporary stand-in.
"I've been training every day," he added. "Working hard and getting fitter every day so it's going well. When you go on tour and play a few games, it gives you a good taste of first-team football and it just makes you want to play more when you get back.
"I know there's probably only going to be one or two opportunities because of the players involved but I can't think like that. I've just got to work hard every day in training and prove I'm good enough to play and, hopefully, get picked.
"A lot has happened in the last year but it's been good experience for me. I keep stepping up a level and, hopefully, that will keep happening and I can progress with England and keep getting my chances here in the first team."