The 2-1 defeat cuts the gap at the top of the Barclays Premier League to 12 points with seven games remaining and the Reds need to get back on track with tricky away matches at Stoke City and West Ham to follow.
Speaking to MUTV after the derby, the former Old Trafford favourite thinks the loss will not have a huge impact on the destiny of the title.
"I think it doesn't matter who we play against with the position we're in now," stated Macari. "A 12-point start on the team below you with that many games left means we're almost home and dried.
"We've only lost four games all season so why are we going to lose four in the space of seven games? It's not going to happen. There's no doubt we're not playing at our very best but who's to say we're not going to pick up at Stoke on Sunday and have a change in fortune until the end of the season?
"The guys are not going to throw it away now, especially after what happened last season. It's almost impossible as there are not enough games to make that many mistakes."
Macari managed Stoke twice and appreciates it will be a hostile atmosphere at the Britannia Stadium as the Potters are battling against relegation.
"It will be a tough game on Sunday," he stressed. "There was unbelievable pressure on Stoke against Aston Villa from the crowd but they will expect United to win and will be right behind their team.
"They realise Stoke are getting in a dangerous situation so it's a big game for us on Sunday and the atmosphere will be unbelievable. The Stoke lads will get cheered on right from the start until the