The Chilean has recovered ahead of schedule from a hamstring injury and is set to face opposition against whom he struck to round off a 3-1 win in March.
But he told his club's website: "I was fortunate to score last year there but they are always tough opponents.
"We go there with the mindset of getting three points and to get a good result after three games in which we deserved something."
South Americans Roque Santa Cruz and Roberto Chen have been limited to fitness work in training after their late returns from international duty with Paraguay and Panama respectively.
Midfielder Duda is a doubt with a back injury and Ivorian striker Bobley Anderson has also trained separately from the squad as he seeks fitness.
Morales is looking forward to being reunited with former Malaga forward Seba Fernandez, now part of Rayo's squad, and said: "Seba is a great person and a great friend.
"I wish him well, but I hope in this game he will not be able to score."
Another former Malaga man set to encounter his old colleagues is Rayo goalkeeper Ruben Martinez, who insists he will treat the game the same as any other.
"It's special," he told rayovallecano.es. "I spent two years with them and I know many people there, but there is no desire for revenge.
"I always try to go out and win. I am not any more motivated just because it is against Malaga. Nor do I have to prove anything."
Malaga finished sixth in the Primera Division last season and enjoyed a run to the Champions League quarter-finals, where they were controversially beaten by Borussia Dortmund.
They have only one point from three games this season but Martinez expects them to rise up the standings again.
"They are reforming as a club and have changed many players in their squad," he said.
"They had a fantastic year last season, with a good run in the Champions League, and have kept a block of that squad together. They are equipped to challenge again."
Alhassane Bangoura was given permission to sit out Friday's training session to deal with a personal issue, while Nery Castillo was absent to have a tooth removed.