The 33-year-old Carrick was injured during United's 4-2 win over Manchester City at Old Trafford last month and will not feature in the remaining matches against Crystal Palace, Arsenal and Hull City.
Fourth-placed United have struggled in Carrick's absence and have lost three successive league matches to allow fifth-placed Liverpool to close the gap to four points in the race for the final Champions League qualification spot.
"We tried everything but now we have to think about next season," Van Gaal told MUTV. "He shall not play any more this season, it's better now to focus for him on next season and being fit to start.
"When you see the stats, it's clear that he's very important but that's also because we have only one right-sided holding midfielder.
"That's what I am saying already in the whole of the season, that our selection is not balanced, and I want to restore that in the next transfer period."
United have started their recruitment for next season, agreeing a deal with PSV Eindhoven to sign Netherlands forward Memphis Depay, who finished as the Dutch league's top scorer with 21 goals.
Van Gaal wanted to wait until the end of the season before adding to his squad but the Dutchman said he was forced to act quickly because the 21-year-old Depay was attracting interest from French champions Paris St Germain.
"He's a goal-scoring winger and there aren't so many of them in the world," Van Gaal told reporters ahead of Saturday's game against Palace at Selhurst Park.
"I was forced to handle (the situation) as a manager because, otherwise, he was going to PSG, that's why I had to sign him and we've done it within one day.
"I want to purchase players after our season and not during the season because it disturbs our concentration for the match."
(Reporting by Michael Hann, editing by Ed Osmond)
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