The Blues agreed a deal to keep the Croatia international at Stamford Bridge this summer after his loan spell from Real Madrid last season.
The 25-year-old midfielder made two assists but failed to score in the Premier League for the west London side last season as the Blues finished in third place in the table.
Chelsea FC are currently serving a two-transfer window ban from signing players but the Blues were able to agree a deal for Kovacic because the loan move was secured last summer.
Nevertheless, former midfielder Merson was clearly not particularly impressed by Chelsea FC’s decision to sign the midfielder on a permanent deal.
Speaking in an interview quoted by Metro, Merson said: “Do you think Kovacic would have signed for Chelsea without there being a transfer embargo?
“I don’t think he scored a goal and they’ve paid upwards of £40m. They’ve signed him because they need another body, surely?
“It’s not all about this year, it’s a three-year contract, and as a Chelsea fan it feels like a good opportunity to steadily, steadily bring these players through.
“One at a time, not bringing a four or five and then suddenly Chelsea are a mid-table team.”
Chelsea FC appointed Frank Lampard as their new manager last week on a three-year deal.
The ex-midfielder takes over from Maurizio Sarri, who opted to leave Stamford Bridge to become the new Juventus manager last month.
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