Northern Ireland international Carroll had played in six consecutive games for The Red Devils after Sir Alex Ferguson opted to rest Howard.
But the United States keeper was restored to the team for Tuesday's Premiership victory over Charlton Athletic and marked his return with a clean sheet.
Howard now appears to be back in pole position to be United's keeper in the FA Cup final against Millwall in May.
Carroll admits he was bitterly disappointed to be dropped and is bracing himself for merely being a substitute at The Millennium Stadium.
"I was very surprised but what else can you do, you have just got to get on with it," said Carroll. "That's football and I was disappointed not to be playing.
"There's only four games left so we are running out of time. Tim's got his position back now and we have just got to get on with it and see what happens.
"That six-game run was the longest I have had since I came here three years ago and I thought I might have got a bit more but I have just got to pick myself up and get on with it.
"You just have to keep working hard and prove you are good enough to play in the FA Cup final."
Meanwhile, the transfer speculation concerning United continues apace with one played linked with a move to Old Trafford and one tipped for the exit door.
The Red Devils are reportedly keen on Monaco full back Patrice Evra, who has shone in the UEFA Champions League this season.
Juventus are rumoured to have first option on the France Under-21 international but Evra could also be the answer to fill in at left back for United.
Reports also suggest that Scottish champions Celtic are ready to move for Ole Gunnar Solskjaer after a swoop for Roy Keane was readily dismissed by all parties.
With Henrik Larsson leaving Parkhead in the summer, Martin O'Neill will need to reinforce his attack with Norwegian international Solskjaer mooted as a target.
Solskjaer is still struggling to regain his match sharpness after a lengthy lay-off with a knee injury and is a valued member of Ferguson's squad.
