Mourinho has been linked with a return to the Bernabeu since being axed by United in December.
And Calderon declared: “I understand Mourinho will sign a deal for the remainder of this season and for another three years, with a net salary of £17m per year, possibly as early as Monday.
“He will return because something needs to be done and president Florentino Perez believes Mourinho is the best man he can get at this time — one of the worst periods in the club’s history.”
Mourinho spent three years at Real between 2010 and 2013, coming away with just one La Liga title to his name.
But in a time when Barcelona were arguably playing some of the best football ever seen, this was not a bad return.
The decision to bring Mourinho back comes after former boss Zinedine Zidane is said to have declined the chance to return to the club.
The Frenchman resigned as boss after guiding the club to three consecutive Champions League titles.
He is said to have fallen out with president Florentino Perez after he allowed Cristiano Ronaldo to leave the club instead of Gareth Bale.
Calderon added: “Mourinho will be the perfect shield against the unhappiness in the media, the fans and the players.
“But it will not be easy and I predict it will be very difficult over the next three months.”
Real currently sit third in La Liga, eight points behind Atletico Madrid and 15 behind table-toppers Barca.
With nothing else left to play for this season, the best the team can hoe for is to restore some pride ahead of the summer.