The Dutch full-back made his first start in two months for the Red Devils as they sealed top spot in Group A with a 1-0 victory at Old Trafford.
Despite being given few chances at the club following his arrival from Vitesse in 2012, Buttner believes that he put in a good display for the team on this occasion.
"I think I did well in my first full game for months," he told United's official website. "I make sure I am always ready. Sometimes players get injuries so I always train hard to make sure I'm ready to play."
Buttner and his teammates continue the defence of their Premier League title on Sunday when they travel to Aston Villa.