The club last won a trophy in 2012-13, when they romped to the Premier League title in Alex Ferguson's last season in charge, and have struggled so far under manager Louis van Gaal.
Saturday's 2-1 defeat by Sunderland led the Dutchman to all but rule out their chances of finishing in the Champions League positions.
"The important thing now, I feel, is to win trophies again this season," Rooney told British media.
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"Obviously the Champions League is massive for this club and it was disappointing to go out of it. But our main aim has to be to make sure we can get in that top four."
United failed to emerge from the Champions League group stages and slipped into the Europa League, an outcome derided by fans and former players alike.
Rooney, however, said the club could not afford to take the opportunity to win silverware lightly.
"It would be great if we can win (the Europa League)," he added. "It's not where we wanted to be at the start of the season but it's where we've found ourselves so why not go and try to win it.
"This is more or less a new team so for ourselves, as a team, we need to win something. The fans want to see us win something again."
(Reporting by Simon Jennings in Bengaluru; editing by Sudipto Ganguly)
