Chelsea ended Mourinho's six-year exile in Italy and Spain on Monday when they reappointed him manager and he will be officially unveiled at a press conference at Stamford Bridge next Monday.
"The Champions League is a thermometer of world football and English football was out of the competition too early," he told Chelsea TV.
"People were speaking about the level of the Premier League going down compared with other countries, but I don't believe that. Sometimes things happen when there are no reasons. But the Premier League is still a fantastic competition and I believe five or six teams are very strong.
"When I was here before it was more about us, Man United and Arsenal and after that there was a gap to the other teams. Now you can put five or six teams in the same plan, aiming to reach the Champions League spots which is very difficult, with those with more ambition aiming to win the Premier League. The competition will be fantastic and I hope I can beat the other clubs."
While the Portuguese's first reign ended in acrimony after his relationship with owner Roman Abramovich soured, his arrival heralded the start of the most successful period in the club's history.
The summit of his achievements were Premier League crowns in 2005 and 2006, and his track record of domestic success - he has also won championships in Portugal, Italy and Spain - have raised expectations he will break the three-year duopoly of Manchester United and City.
Chelsea fans will expect Mourinho's return to be accompanied by a spending spree as Abramovich arms his manager with the funds to reclaim a title they last won in 2010 when Carlo Ancelotti was at the helm. But the 50-year-old insists that drawing the best from his existing squad will be his most pressing concern and refuses to prioritise any silverware.
"We have to improve the team, but when I say improve the team people are already thinking about how many millions Chelsea will spend. When I say improve the team, I mean through work," he said.
"My work has to improve players and improve the team. If I don't do that I am not happy with myself. If after that we can improve the team by buying a couple of players it is fantastic, but I have to improve the team and the players with my work."
Source: PA
Source: PA