Ole Gunnar Solskjaer urged Manchester United to show a killer instinct against Arsenal after scoring just 10 goals in their eight matches in all competitions this season.
"We need to score more goals, definitely. We are working on improving the relationships, the pattern, the understanding," Solskjaer told reporters.
"We started at one end with the foundation. We have done great defensively, but of course we are not happy with the return going forward."
"And we wouldn't mind a few goals from set plays and midfield. The forwards are always going to produce goals."
"Of course when we let Alexis and Romelu go, it doesn't take a rocket scientist to see that the next time we recruit, we will be looking for some creativity and goals."
The departures of Lukaku and Sanchez were no surprise, but Solskjaer said United did not just want to bring in a stop-gap replacement like Fernando Llorente, who has gone to Napoli, or Juventus's Mario Mandzukic.
"We could not get the striker we wanted," Solskjaer said.
He added that leaders Liverpool and Manchester City in second place are already 13 and eight points clear of them respectively, but Solskjaer believes the rest of the top four can be caught.