After easily winning back-to-back Premier League trophies in his first spell at Stamford Bridge between 2004 and 2007, Mourinho managed third position upon his return to Chelsea last season.
Chelsea only finished four points adrift of champions Manchester City, while London rivals Arsenal were a further three behind.
"In England it is even stronger now than in my first period," Mourinho said in an interview with BT Sport.
"Even more now because when I first came Man City didn't have this financial situation they have now.
"Even Tottenham at this moment, all the top five or six. In this moment can you tell me who is going to win the Premier League?
"You can't tell me. You can try to tell me but can you say which one of the top five is going to be outside the Champions League? You can't say. This is what I want."
"Last season was important for me and for the players, but I think we did a fantastic job in the transfer market – we went exactly to the targets we want to go," he said.
