United have been significantly outscored by all of their top-six rivals and Mourinho admits he is frustrated by his side's inability to convert territory and possession into goals.
"I have to agree with you that we don't score enough goals," said Mourinho. "Some of our players from these attacking creative positions they could - they should - score more goals.
"I understand what you are saying. We attack so much and with so many players, and so many players have the freedom in our dynamic to reach scoring positions.
"When you see the number of goals we score, there is not a true relation between our attacking production and the number of payers we put in attacking positions and the number of goals we score."
Ibrahimovic, at 35 years old, is comfortably United's top scorer with 19 goals, 14 of which have come in the league.
Mourinho said: "When you speak about Zlatan's goals you should always add 14 goals and one penalty in 31 matches played in England in all competitions. You should always add that extra item.
"In almost every team the striker is the top scorer, I think so, unless you have another player with a special feeling to score goals coming from another position or you have another player scoring six seven or eight goals from penalties that is normal to happen."