Ajer has been impressive for much of the campaign, but has arguably stepped up significantly in recent weeks. It is now surely fair to say that the Norwegian is establishing himself as Celtic's best centre-back.
But a bigger surprise has been the form of Simunovic. The 24-year-old returned to the team at the start of the month, and it is starting look like he is rediscovering the outstanding form that he showed during the early stages of his Parkhead spell.
Both were excellent at the weekend as Celtic secured their spot in another Scottish Cup final with a 3-0 win against Aberdeen. And McAvennie was full of praise for both men, also noting the piece of skill that Simunovic produced in the early stages of the tie.
“Ajer has turned in to a wonderful player and I was impressed with Jozo on Sunday. I didn’t think he had the step-overs in his locker," he told Herald Scotland.
With Dedryck Boyata out of contract and Filip Benkovic's loan spell coming to an end, centre-back is likely to be one area of the squad that the Hoops boss will need to address over the summer.
Signings will definitely be required and Simunovic's injury record will be a concern, but there have been signs in the last few weeks to suggest that he and Ajer could potentially form the kind of partnership that Celtic come to rely on for years to come.