Arsenal have made a new £25m bid for Celtic left-back Kieran Tierney, with Unai Emery desperate to bolster his defence at all costs. The Scot has been one of Arsenal’s primary transfer targets this summer, with the Gunners seeing an initial £15m bid knocked back by Celtic. Now, BBC Sport state that Arsenal have lodged an improved £25m bid for Tierney, which would make him the most expensive sale in the history of Scottish football. The Gunners were thought to be preparing a bid of £20m, but with add-ons which would take the overall value up towards £25m. However, it now appears as though they have offered the full £25m in its entirety to try tempt Celtic to part ways with their star. Emery was keen for Tierney to join up with the squad before they left for their pre-season tour of the USA, but Celtic stood firm on their valuation of Tierney. The 22-year-old, who already has 170 appearances for Celtic under his belt, is currently recovering from hernia surgery, although it is believed that he could recover in time for the beginning of the upcoming season. Napoli have also been linked with the Scot, with the Serie A side said to be ready to sell Mario Rui to make space for Tierney in their squad. Rui is nearing a £15m move to Benfica but, with that deal yet to go through, Napoli are yet to make an official approach for Tierney. However, Carlo Ancelotti is believed to be a huge fan of Tierney, so news of Arsenal’s latest bid may force the Partenopei to make an offer of their own. In what was an injury-hit season for Tierney, he made 20 Scottish Premiership appearances for Celtic last year and managed to rack up five assists. Arsenal are seemingly not concerned by his fitness struggles, as they remain desperate to get this deal over the line as soon as possible.