The teenager from Argentina was promoted from the youth team to the first team earlier in the season and shot to prominence by scoring winning goals against Real Sociedad and Fulham in November.
He set up Marcus Rashford's winning goal against Manchester City last month but has not scored since November and spurned a couple of good chances in Wednesday's 2-2 draw at home to Leeds, including having a shot cleared off the line.
"I think he is a threat as we saw on Wednesday, he had good actions, he was lively, he created great chances but he had to score. Finally, it is about that - that you have an effect," Ten Hag told a news conference ahead of another match against Leeds in the Premier League on Sunday.
"As a striker, you have to be on...the scoring list, the assist list, the key action list.
"As a Manchester United player, we expect you to have an impact, to influence the score, the result, to have a positive influence on the game by scoring goals and having assists."
The manager said Anthony Martial, Antony and Scott McTominay were unlikely to recover from injuries in time for Sunday's match, which midfield linchpin Casemiro is suspended for. He will be serving the second game of a three-match ban for being sent off last Saturday against Crystal Palace.