Messi also spoke about his potential club partnership with new Barca signing Neymar.
"I think the Spanish league is difficult anyway, and will continue being difficult," Sky Sports News quotes Messi as saying.
"Mourinho was a great coach but we know that Ancelotti is equally great. I think Mourinho will also succeed back at Chelsea because he's a great manager.
"I know Neymar is a great player who will bring a lot to Barcelona. God willing, we will be able to play together at Barca."
Messi is currently under investigation for tax evasion charges.