David Moyes says Chelsea are as good any team in the Premier League, despite Antonio Conte's side trailing leaders Manchester City by 11 points.
Chelsea have experienced a stuttering start to their title defence, losing three of their opening 15 games after only suffering five defeats throughout the whole of last season.
But West Ham manager Moyes was keen to praise the reigning champions ahead of their Saturday lunchtime fixture, which is live on Sky Sports Premier League.
"I'm not an expert on Chelsea but I think how they played last year was fantastic," Moyes said.
"I think they've got numerous good players, I think maybe just a slow start to the season might have just caught them out a little bit.
"Manchester City have been so strong from day one, but I think Chelsea on their day are a match for anyone in the Premier League.
"They proved that last year and I think they are probably doing that a bit more now as well."
Both Moyes' former clubs Everton and Manchester United feature on Derby Day this Sunday, live on Sky Sports Premier League, and the Scot was keen to extend his support to both sides.
"They're really hard to call the derbies, I think the Manchester derby is the two best teams playing against each other," he added.
"It might favour Manchester United being at Old Trafford because of the home advantage, but Manchester City have been good wherever they've gone this season.
"I think at Everton it was always difficult going to Anfield, over the years we played against some great Liverpool teams.
"By the end of my time we had managed to finish above Liverpool the last two years in a row, but I've got to say from where I have been I want Everton to win and I want Manchester United to win."