City are determined to sign Sanchez from Arsenal despite seeing a move fall through on deadline day.
And Diario Gol say any move is expected to see Aguero then seal a return to Spain, where he previously played with Atletico Madrid.
Should he end up staying put, then a transfer will supposedly happen in the summer.
And Real think they can land him for a fee as cheap as £35million.
Messi is reportedly concerned because he does not want a player of Aguero’s calibre playing for Barcelona’s fierce rivals.
But the 30-year-old will be powerless to stop a transfer from happening.
ESPN pundit hails Messi as the world's best player right now
GETTY
Messi: Barcelona star does not want Real Madrid to sign Sergio Aguero from Man City
Invalid email
We use your sign-up to provide content in ways you've consented to and to improve our understanding of you. This may include adverts from us and 3rd parties based on our understanding. You can unsubscribe at any time. Read our Privacy Policy
Meanwhile, Sky Sports pundit Tony Cottee thinks Sanchez will join City - if playing football is his biggest priority.
“Purely from a player’s point of view, he needs to sit tight if it’s about money," Cottee said.
“He’s just got to sit tight because at the end he’s going to get a stack-load more money at the end of the season by being a free transfer than if he moves now. If it’s about money.
“If it’s about football, he’ll sign for Manchester City and move on.
“If it’s about money, he’ll sit tight and wait until the end of the season.