For all the focus on Arsenal’s gaping hole at left wing, the leaky backline needs addressing – and fast.The absence of William Saliba due to a back injury is problematic for the Gunners, highlighted further after this pre-season friendly against Borussia Dortmund.The north London club have conceded six goals in two matches, not helped by a lack of cohesion at the back.Riccardo Calafiori’s adventurous runs forward and a midfield with a desire to attack left spaces for the Borussia Dortmund frontline to exploit – and they did.Take their two first-half goals. Samuele Inacio was easily played through in the area, to poke the ball past Kepa Arrizabalaga.Then on 29 minutes, Konstantinos Karetsas navigated his way into the area before curling the ball high into the net. Arsenal have conceded six goals in two pre-season matches and must address their leaky backline fast Mikel Arteta’s side are set to start the season without the influential William Saliba through injury The Gunners are in the market for a centre back to strengthen their options alongside GabrielThe ease by which Dortmund were able to breach the defence stood out because of how strong this team typically are defensively. It certainly will have incensed Saliba from where the Frenchman was watching.His absence for the coming months shifts the team’s balance, which the north London club are keenly trying to address.It’s understood Arsenal are in the market for a centre-back, with Cristian Romero an option that has been assessed.The connection between the Argentine and assistant coach Gabriel Heinze is an influencing factor. Though Tottenham, as expected, are staunchly against the prospect.Saliba’s positioning and ease on the ball may not be replicated, but a defender mirroring those traits would help plug the gap for now.On Saliba, Mikel Arteta said: ‘When he’s been available, he’s hit form. And the stats are incredible. So we know that we lost a massive player. The same with Jurrien (Timber). Some of these seven or eight players weren’t here today with us.’At the other end of the pitch, Christos Tzolis clearly fancies his chances as Arsenal still hunt a shiny new forward after losing out on Vinicius Junior.Tzolis is viewed internally as a winger with a high ceiling, one who can and should push for a first-team slot in the coming seasons. New signing Christos Tzolis looks eager to take his chance on the left wing after Arsenal missed out on Vinicius JrYet, aware of the circumstances, the Greek is pushing hard to stake a claim right now. After a mixed first half, Tzolis kept trying to get on the ball and make things happen.His ability to target the byline or cut inside makes him a tough proposition to face, the opposition at times stuck on which way to shield him towards.The winger’s assist for Ethan Nwaneri, driving towards the byline to put the ball on a plate for his team-mate, pressed home his attributes.The opportunity is there with Gabriel Martinelli, who has not reached the heights of his breakthrough 2022-23 where he struck 21 goal contributions, a possible outgoing this summer.That was reinforced by Arteta’s substitutions, bringing on Martinelli after 78 minutes, along with Gabriel Jesus and Fabio Vieira who are already at the exit door.Arsenal are open to Martinelli leaving if the right money is offered, with Galatasaray interested.Fans excited as Guimaraes adds to formidable midfieldTrotting up the Emirates tunnel with a cluster of club videographers encircling, Bruno Guimaraes emerged. Wearing baggy jeans and an Arsenal jersey, he raised his arms aloft to cheers.It wasn’t quite the unveiling of say Eberechi Eze last season ahead of Arsenal’s first home league game against Leeds. The circumstances were different, that game a match with ramifications rather than a friendly.The Gunners also had the added bragging rights of beating Tottenham to the signing of Eze.So the noise and reaction was understandably different, yet very clear: the Gunners faithful are excited about the Brazilian’s arrival. He’s the club’s first marquee signing of the summer, ending a long saga.The midfield is already a formidable concoction featuring Declan Rice, Martin Odegaard and Martin Zubimendi.Adding the aggressive edge and propensity to play ambitious passes provides a layer which the Gunners can lack at times.Add a new attacker and centre-back to the mix, Arsenal will take some stopping. Bruno Guimaraes was unveiled in front of the Arsenal fans after his £75m move from NewcastleGyokeres and Havertz offer Arteta another optionIt’s starting to come together, finally. The pair who initially were viewed as separate commodities are slowly becoming an option of being in the same line-up.Arteta planned to have Kai Havertz as his No1 striker last season before the German’s knee issues paved the way for Gyokeres.With Havertz now fully fit, Arteta has started the pair together for three consecutive pre-season matches, testing whether they can complement each other for the new season.There is more work to be done in understanding each other’s positioning and runs. But there were enough signs here to suggest it can be an option.On 20 minutes, a sublime Odegaard through ball released Havertz down field. He tried squaring it to Gyokeres, before goalkeeper Alexander Meyer snuffed the attack out. Viktor Gyokeres linked up with Kai Havertz in attack with the pair showing enough to give Arteta another option ahead of the new seasonThe pass should’ve been better. But the thought was there.Minutes later, another Odegaard pass reached Havertz, his cross headed wide by Gyokeres. Across the match the pair kept trying to look out for one another to link up.They are friends off the pitch and there is a willingness to work in unison, rather than a stubbornness to be the main man.It will be interesting to see how Arteta utilises the pairing once the season officially starts.