Gianfranco Zola has said that he believes both Arsenal and Manchester City can challenge Chelsea for the Premier League title next season.
However, the former Italy international excludes Manchester United from the list, saying that he is unsure whether they will be able to "step up and improve".
Zola, who has managed both West Ham United and Watford, expects Jose Mourinho to mount a strong defence of the title but thinks that it is up to the surrounding teams to improve and challenge for the crown.
"I know Chelsea are going to be strong – I have no doubt about that. I think the question is not what Chelsea can do, it's what can the others do to challenge them?" Zola told Sky Sports News.
"City will be stronger next season but I'm expecting Arsenal to be more competitive as well. I thought in the second part of the season Arsenal were outstanding. They impressed with the way they were defending, something that was not their best point.
"Regarding Manchester United, we know the potential of the club. The point is I don't know if they will be able to step up and improve the level of performance. They will be a good challenge for Chelsea as well but I think City and Arsenal will be more competitive."
Chelsea finished eight points clear of second-placed City last season, securing their fourth Premier League title.
