Taylor Walker replacement Lewis Johnston is also under a ligament injury cloud Lewis Johnston walks to the club rooms on crutches after injuring his knee playing for North Adelaide. ADELAIDE'S search for a new attack will be complicated today if the appealing option of Lewis Johnston is lost to the precise goalkicker needing knee surgery. While Crows key forward Taylor Walker today has his right knee reconstructed, Johnston will have scans on his left knee to determine if he also has ligament damage requiring surgery. This would further deplete Adelaide's cards in attack where key forwards Kurt Tippett (defected to Sydney) and Walker have been lost to injury and small-medium forwards Jason Porplyzia, Ian Callinan, Jared Petrenko and Graham Johncock have spun through a revolving door at selection because of poor form. This has taken the Crows' highest-scoring attack in the club's history from an average score of 106 points in 2012 to 88 this season. Adelaide forwards coach Mark Bickley yesterday did not hide his eagerness for Johnston to stay in his planning for this season. "We're not sure if that knock to his knee has done damage to the ligaments," Bickley said. We're sweating on the scans because Lewis is clearly the size profile we are looking for ... and he is a beautiful kick. Johnston , who was traded to Adelaide in 2011 when the Crows wanted to move on Tony Armstrong, stands at 193cm - taller than Walker (192). He was considered a contender to replace Walker before Adelaide coach Brenton Sanderson opted to call up ruckman-forward Shaun McKernan to work a tandem with Josh Jenkins and Tom Lynch. He also turned the Crows line-up upside down with defender Matthew Jaensch in Adelaide's forward six. By kicking 11.12 in the 11-point home loss to Hawthorn on Saturday, the challenge remains to find a forward set-up that can deliver more, particularly when Adelaide's midfield is under-performing. "Andy Otten was fantastic in defence, but maybe he is an option (as a forward)," Sanderson said. He looked sharp in that role last week (when he covered for the loss of Walker. We will try to settle it down. We will try to find a combination that looks comfortable. But we might have to make some adjustments. Adelaide's attack worked to the supply of 50 inside-50 entries yesterday. Key forward Josh Jenkins was the most productive with 2.4 - and he appeared more assured while his role was simplified to being a go-to forward. Sharing ruck duties with Sam Jacobs fell to McKernan, who finished with no score. Adelaide's other major challenge - after falling to a 2-4 win-loss count - is dealing with the continued ineffective tackling of so many Crows. "We won the tackle count (54-50), but it was obvious to the naked eye that when they tackled us, it stuck - and when we tackled them, they were able to shrug their way out of it or still get an effective disposal away," Sanderson said. It is an issue that continues to come up for us - and an issue we'll continue to work on. Adelaide reported no injury with the 22 who played against the Hawks, but utility Ricky Henderson was forced out of the line-up by a calf strain. He faces to a test to play against Greater Western Sydney on Sunday.