The Red Devils have won all four of their Group H games and have progressed to the last 16 of Europe's premier club competitions.
"People have been saying we can play better for the last six or seven years," he is quoted as saying by The Mirror.
"We know we're capable of playing better than we are, but results are the most important thing.
"We're happy with where we are. We're delighted to have won all four games and finish top of the group. We know we can play better than this, but we're happy that we're winning."
United are currently at the top of the Premier League table with 24 points from 10 matches.