Real are still believed to be chasing the Tottenham playmaker, while midfielders Kaka and Nuri Sahin are expected to leave the Bernabeu.
But Mourinho feels it is the determination of the current group that can drive the Spanish champions on to future success – without the need for lots of additions.
“We are hard at work preparing because we are well aware of the fact that it is not going to be easy, quite the contrary,” Mourinho told Fox during Real’s pre-season tour of the United States.
“The team is almost complete,” added the Portuguese, who helped end Barcelona’s three-year grip on the La Liga title last season.
“They are special players, we have a lot of the best players in the world and my team’s motivation when faced with new challenges never ceases to surprise me.”
Modric is keen to leave Spurs but the club’s £40million asking price for the 26-year-old Croatia international is proving prohibitive to a deal.
Real defender Sergio Ramos believes the current squad is strong but admits he would welcome the arrival of Modric.
“There haven’t been many departures or signings, but we are open to everything,” Ramos told reporters.
“We’ve got a great squad, with amazing footballers, and one or two more will join.
“I like football and good footballers and Modric is one of them. He currently doesn’t play in this team and I can’t say any more than that. If he joins he’ll bring something to the team.”