On Tuesday Manzano was named as the successor to Joaquin Caparros, who was sacked following the team's 3-0 defeat to Real Sociedad last weekend, a result which left the club second from bottom in the league table.
This is the third time Manzano has coached Mallorca and the appointment was not entirely welcomed by fans, but Casadesus has spoken of the importance of backing the new boss.
"On Saturday, more than ever, everyone has to get behind the players and the coach," he said in a press conference on Thursday.
"We have a new coach, everything starts from zero now and we have to charge our batteries, from the goalkeeper to the last man," he added.
The forward said he thought having a new coach would help the team and, despite admitting they were in trouble, he believes his side can still avoid relegation.
"No one has enjoyed being in the situation we are in but it's true that we needed a change and now we've got that, I just hope it's for the best and that the team improves," he added.
"We are in a delicate situation, but there are enough games left to turn it around. We have to continue working as we have been this week and do the new things the new coach has asked of us."
Mallorca goalkeeper Dudu Aouate could return to the starting line-up on Saturday after recovering from injury, while Alan Hutton and Tomer Hemed have both returned in perfect condition from international duty with Scotland and Israel respectively.
Osasuna coach Jose Luis Mendilibar, whose team are outside the relegation zone and four points clear of Mallorca, stressed the importance of picking up points away from home, beginning with Saturday's match.
The Navarrans have won just five points in 10 games on the road this season, a record Mendilibar said his team must improve on.
"We cannot just survive on our home form, because there'll be some moments in which we make mistakes and lose games at home," he told reporters.
"We've began the second half of the season with two games at home in which we've got good results [a goalless draw with Real Madrid and a 2-1 win over Deportivo] but we cannot just trust in our home form, I won't accept that.
"We have to pick up points wherever we play so we can get to our objective of 40 points."