"We lose a very important legend in Sergio Aguero," Al Mubarak said on Tuesday. "They are very hard shoes to fill, but I'm confident that we will find the right player to fill those shoes.
"There are other areas within the group, within the team that obviously need investment. Not too many. It's not about numbers, it's about quality.
"One of the things I've learned over the years is you need to constantly bring in talent into the team, refresh and particularly when you are at a high level and when you're on the top."
Al Mubarak said City, who also won the League Cup, will not stand still despite their domestic success.
"Having won the league, it is not the time to sit back and be content. That would be your biggest mistake," Al Mubarak added.
"This is the time to send a strong message, that there's no contentment, that you're not satisfied with just winning the league."