The Red Devils have won just one of their last five games in the top-flight, leaving them 12th in the table after six games - eight points off the pace set by leaders Arsenal.
Dutch left-back Buttner was preferred to Patrice Evra for the home game against West Brom on Saturday, having also played the full 90 minutes in the Capital One Cup victory over Liverpool in midweek.
However, Buttner and his team-mates were on the end of a shock reverse to Albion as Morgan Amalfitano and Saido Berahino struck in the second half to hand the visitors a 2-1 victory.
"We're very disappointed to lose the game. It is very disappointing for everyone," said the 24-year-old.
"Normally we have to win this game at home but no, I don't think it is a crisis.
"We have lost games but we have to focus and fight in every game to win it.
"Of course the crowd want to see Manchester United winning - the players want that too."
Buttner has backed United to quickly turn their domestic form around, with a clash at Sunderland next up on Saturday evening after Wednesday's Champions League trip to Ukraine to face Shakhtar Donetsk.
"Our season starts now and we can win many games," said Buttner. "You have to trust the players and everyone.
"I think we can do this as a team. We are going to win games, I am sure."