Rashford had 10 shots on goal in Thursday’s 1-0 win over Omonia Nicosia in the Europa League but failed to score and it was midfielder Scott McTominay who rescued United with a stoppage-time winner.
“He knows that he has to be more clinical,” Ten Hag told a news conference.
"When he has such good movement, makes such good combinations, has such good actions, he has to finish. But sometimes it’s not your night, it’s the form of the day but it can change to another game.
"He is on a very good run, he proves that with the chances he creates. The last two games he was a little bit unlucky but I say save it for the coming week."
Rashford is United’s top scorer with five goals in all competitions but needs to be more prolific if Ten Hag’s side are to push for a top-four finish in the Premier League, with his fellow forwards also lacking consistency.
Cristiano Ronaldo has only scored twice this season while Anthony Martial has struggled with injuries and is a doubt for the Newcastle match after being forced off after only 29 minutes against Everton last Sunday.
The exception is Brazilian forward Antony, who is the first player in the club’s history to score in his first three league games, netting against Arsenal, Manchester City and Everton.
Ten Hag backed his attacking players to improve their goal count but said he wanted players from all positions to contribute to scoring.
“I’m confident, mostly, that my players will score. We have players in the squad but we are divided because we have many goalscorers across the offensive department but we also need something from midfield and defensive departments,” he said.
The Dutch coach also said the last-gasp win over Omonia would lift his side’s spirits ahead of a gruelling week of Premier League fixtures against Newcastle, Tottenham Hotspur and Chelsea.
“It gives another impulse in the team. The belief and the spirit is already good but it will give a push for the rest,” he added. “We are against tough opponents but we are looking forward, it’s a real test for us as a squad.”
