Former Celtic striker John Hartson issued a warning despite the club’s impressive win over Jablonec in the Europa League last night.

Celtic picked up a 4-2 win over the Czech Republic outfit, but their defensive flaws were brutally exposed during the game.

They must look to improve defensively if they want to challenge for the Scottish Premiership and progress in Europe this season.

Ange Postecoglou must work hard in the remaining days of the transfer window to make the necessary adjustments to his back four.

Hartson tweeted that the Hoops were poor at the back and urged fans not to get too carried away with the result.

4 goals 4 different scorers for Celtic.. good Win away from home in Europe yes.. but defensively we are in disarray ! Don’t kid ourselves..if you can’t defend you don’t win.