The Belgian midfielder joined the Premier League champions from Everton on the final day of the transfer window.
Giggs told the team's website: "Marouane is proven in the Premier League so he doesn't need any bedding-in time when it comes to learning the English game. That's a big positive. He brings us strength, height at set-pieces and goals from midfield.
"He was really keen to join us and that's always a great quality, when a player is desperate to play for United they're usually determined to make the most of it when they're given that chance. I have no doubt he'll enjoy himself here, playing in the Champions League, playing in the big games.
"He was someone who always warranted a mention in our team-talks when we played Everton. In the 4-4 draw at Old Trafford in April 2012 he was a real handful and scored against us again on the opening day of last season, so he was definitely someone we focused on when we played Everton"
United face Crystal Palace at lunchtime.