United fell to a 1-0 loss at home to Arsenal on Monday (AEDT), ending a slight upturn in form and leaving it with only seven points from their opening six Premier League games and languishing in 15th place.
Ole Gunnar Solskjaer's men have won just one of its five home matches this term, a run that includes a 6-1 Old Trafford hammering at the hands of Tottenham.
And while United has impressed in the Champions League with two wins from two, Rashford admits his boyhood club's disappointing domestic form is taking its toll.
"This is something I've been doing since I was a kid and something I love to do," he said.
"For it to maybe not go as well as I planned it to be, it's heartbreaking. I think it's a period where we need to get back to basics and find ways to win games."
Rashford said: "It's been tough. Obviously we've had a lot of big games and games we need to get points in. It's been a bit up and down but it's like that sometimes.
"It's all about sticking together and finding a way to win games and really picking up the belief.
"We always bounce back when we don't do so well and I think it's another one of those times. We have to come together as a team, get back to the basics, and win games."
United followed up its joint-record Premier League defeat to Tottenham with three wins and a draw in their next four matches, scoring 11 goals in the process.
Five of those goals came in an impressive win over RB Leipzig in the Champions League, with Rashford coming off the bench to score an 18-minute hat-trick.
It has also beaten Paris Saint-Germain on the continent this term and Rashford is hoping to keep that run going with victory over Istanbul Basaksehir on Thursday (AEDT).
"It was obviously a proud moment [getting the hat-trick], something you dream about as a kid," he said.
"I was very happy about it but the result was obviously a big result for us in terms of qualification in the Champions League.
"We need to back that up in the next game and hopefully get another three points.
"PSG was another tough game for us but we found a way to win the game. Sometimes, that one moment is all it takes.
"We definitely need to do that more and we need to start games a lot stronger than what we have been doing in order to get the points."
United have lost their last two away games against Turkish opponents in European competition - 1-0 v Galatasaray in 2012 and 2-1 v Fenerbahce in 2016.
Rashford, who has two goals in the top flight this term from seven shots on target, is looking to put that right at the Fatih Terim Stadium.
"As a club, that's our next focus now," he said. "We've analysed the Arsenal game and we can't dwell on that for too long, otherwise it will affect our next performance.
"It's important we go there with a fresh mind, a clean slate, play well and win the game."