The youngster scored his first Premier League goal in last Saturday's 4-0 win against Stoke City and the Spanish boss has backed his compatriot to find the net more regularly as he adapts to English football.
Martinez told the Liverpool Echo: "It's only a matter of time before he starts scoring them more often. I'm never worried about him missing the chances, it's more him getting in positions we can take advantage of.
"You're looking at the tactical aspect of how to get him in those positions, and he does that with ease.
"Gerard is getting in great positions and became a real worry for the United defence when he came on. He creates a threat time after time."
The Blues travel to league leaders Arsenal on Sunday.