Olivier Giroud, Tammy Abraham and Timo Werner have shared the duties in spearheading the Chelsea frontline this season.
The Frenchman is 34-years-old and his current stint at Stamford Bridge expires in the summer, while Werner, who has played more of a wider role, is struggling with his form.
Former top flight defender Delaney is still not sold on the quality of Blues academy graduate Abraham and he feels Chelsea boss Tuchel should find a new number 9 in the summer, someone who is of the same ilk as Manchester City star Aguero.
At the moment Tuchel has an embarrassment of riches on both wings and in the number 10 role, according to Delaney, but he stressed a proper number 9 is missing, that can make the most of any chances in the box like Aguero.
“Very difficult to play someone like Olivier Giroud week in week out, European football during the week and this [Premier League]”, Delaney told Off The Ball.
“As you get older you cannot just keep going to the well and I think [Sunday] was just kind of a bridge too far for me, very, very difficult.
“He is an old-fashioned number 9, he just wants to stay on the pitch and get service and then all the young lads run around him.
“Tammy Abraham, I do not know what is going on there, maybe he is not kind of at that level, the required level.
“Timo Werner is slowly; I suppose finding a little bit of form after [a barren run].
“[Even though he is playing more on the wide left], maybe he was brought into play as a number 9 as well.
“So, they have enough wingers and number 10s really.
“May be Tuchel does not want Werner playing as a number 9.
“So probably one player they are missing, and maybe Tuchel will say well we had enough possession we put enough crosses in, you know if I had a real number 9, a Sergio Aguero type player, we would have got some goals [against Manchester United].
“And that probably is a valid argument, but he has not, so he has to figure out a way to get all those great diminutive number 10s higher up the pitch in better positions to score goals.”
Chelsea have been linked with Borussia Dortmund hitman Erling Haaland, who has a release clause that will come into effect in 2022, but is likely to cost big money in the summer.