The Spanish forward was a fan-favourite at Real before moving on to Liverpool in 2005, and was speaking as he returned to his former stomping ground with Marseille for their Champions League Group C match on Wednesday.
The 33-year-old helped knock Real out of Champions League at the quarter-final stage in the 2003/4 season, while on loan with AS Monaco, but gave away little on how best to achieve a similar result to his new colleagues.
"There is no recipe for beating Real Madrid. You only have to hope they don't have a good day and make the most of it," Morientes told a news conference.
"It's a difficult place to play for any opponent, not only those who are appearing for the first time. We'll have to be 100 percent alert."
The Bernabeu is the venue for the Champions League final next year and Real's six wins from six games in all competitions so far has helped fire expectations that they are on course to claim their tenth European Cup.
One of their new high-profile signings, Kaka, sought to play down the euphoria.
"It isn't easy to win the European Cup. Everyone is talking a lot and it is as though Real are already in the final," the Brazilian told the club website.
"The team needs to develop and improve in many areas yet."
Real coach Manuel Pellegrini has found himself questioned over his system of rotations, particularly with regards to the forwards, and he has to keep one eye on Sunday's trip to face third-placed Sevilla in La Liga.
But his main problem for Wednesday will be at right back. With Alvaro Arbeloa injured, and Sergio Ramos in the squad but a doubt, Raul Albiol could be asked to move out to the right of the defence.
France midfielder Lassana Diarra misses out with a shoulder complaint, joining striker Ruud van Nistelrooy and defenders Arbeloa and Christoph Metzelder on the injury list.
