Rangers play in the match next month without either of their recognised strikers. Former Norwich flop Kyle Lafferty is cup-tied, whilst Alfredo Morelos is banned.
Roma loanee Sadiq is the only other recognised centre-forward in the Ibrox first-team squad but so far he has failed to make an impression on his manager.
Gerrard warned: "Competition for places is very tough all over the pitch, not just in the number nine position, so Umar's got to fight.
"He's come in as a young boy. I think he's settled in well enough. I think everybody at Rangers has done everything they can and the fans have got behind him.
"But the reality is - and there is no secret in any position - you have got to fight and show myself and my staff that you're worthy of game minutes.
"It can't just be given to you, not at a club like this. So it's over to Umar, the ball is in his court. He has the chance and the opportunity to impress all of us on a daily basis.
"But you don't have to be a rocket scientist to work out that he is going to have to improve if he is to earn some game time.
"[The semi-final] is a fantastic opportunity but just because he is one of the number nines we have got and two are not available, it doesn't mean he is going to feature. You have to earn the right."