Madrid have already secured a last-16 berth after winning each of their opening four Group D matches and, with a five-point advantage over second-placed Ajax heading into the penultimate round of fixtures, they are overwhelming favourites to clinch first place.
With a draw against bottom side Dinamo possibly being enough for Madrid, and perhaps with one eye on this weekend's derby with Atletico Madrid as well, Mourinho is planning on ringing the changes - although the Portuguese insists he is still wary of the threat posed by their Croatian opponents.
Mourinho, whose side won a five-goal thriller against Valencia on Saturday for their 11th successive win in all competitions, said: "It's not a high-risk game where if you lose you are out, but Zagreb will be difficult because in the first leg we played with our best team and we won by the narrowest of margins (1-0).
"They are the Croatian champions and they have 10 points more than the second-placed team in their league.
"I have to make changes in my team because I have very tired players, not because the opponents will be easy."
He added: "We are group leaders with 12 points, with four wins, and we want to be first in the group. We don't know if being first will help us, but it gives us something of an advantage.
"We want to play to win tomorrow, score goals, and entertain the fans in the process."
Mourinho refused to reveal what his line-up would be, but he will definitely be without Kaka, Ricardo Carvalho, Angel Di Maria, Marcelo and Alvaro Arbeloa through injury.
One player who could start is Turkey international Nuri Sahin, who has made only one substitute appearance for Madrid since joining the club this summer because of fitness problems.
Sahin was put forward for the pre-match press conference, and Mourinho said: "Until now, the four players who have gone out in the Champions League press conferences have all been starters. So logic dictates, that could be the case (that Sahin starts).
"I can't confirm the team because the players still don't know the side. It's a basic principle of mine that they are the first to know."
Mourinho welcomes back Fabio Coentrao and has called up youth team goalkeeper Tomas Mejias in a 19-man squad.
Dinamo head to the Bernabeu having failed to record either a goal or a point from their first four group matches but, while they cannot finish in the top two, they still have an outside chance of claiming third spot ahead of Lyon, who are currently four points ahead.
Like Madrid, Dinamo go into Wednesday's match in good domestic form, where they have won nine of their last 10 league and cup matches .
Dinamo coach Krunoslav Jurcic will be without defenders Josip Simunic and Sime Vrsaljko through injuries.