Chelsea lacked focus this season and failed to live up to expectations, former Arsenal and Aston Villa midfielder Paul Merson said.
The Blues ended the campaign in a disappointing 10th place as they failed to qualify for next season's Champions League.
They replaced Jose Mourinho with Guus Hiddink in December with Italy's Antonio Conte to take over at the end of the Euro 2016 Championship.
And Merson says they have been poor throughout the whole season.
"Many people expected Chelsea to be up there defending their title under Jose Mourinho," Merson told Sky Sports.
"But it didn't quite go to plan.
"It's been an incredibly disappointing season for the Blues during which Mourinho lost his job. They've been poor all season and the concentration just has not been there from the players.
"Definitely a season to forget for Chelsea."
