Paul Merson has warned Chelsea that it would be a colossal mistake to sell one of their players currently linked with a potential exit this summer. For Chelsea fans, there’s certainly a fear of the unknown going into the summer. First of all, will the Blues learn from previous mistakes and be smarter in the transfer market? Most importantly, will Mauricio Pochettino still be the head coach in the dugout next season? Journalist David Ornstein told NBC Sports last week that Chelsea plan to review Pochettino’s position as manager once the season is over. The Blues boss made the bizarre claim on F…