Stroll had to miss last week's Bahrain test due to a wrist injury, leaving Alonso and rookie Felipe Drugovich to undertake the initial sorting and development work on the new car.
Alonso admits that he doesn't have enough of a reference to properly analyse the behaviour of the AMR23 and compare it with its predecessor.
While the Spaniard drove last year's AMR22 in November's Abu Dhabi test and in recent Pirelli 2024 tyre development running, Stroll had a full season of race experience with the car.
He would thus have provided valuable continuity in terms of comparisons with the new model.
"We are learning a lot about the car, I think this car is very different compared to last year," said Alonso at the end of the Bahrain test. "We are changing a lot of things.
"Unfortunately we don't have Lance, because that would be a benefit for us. We miss him here because some of the changes we're making to the car, we don't know if it's this car, or it's just an Aston Martin thing that for me feels different.
"So it's not ideal, but hopefully he can give us some feedback soon, and we can make some progress."
Expanding on the areas where the team is lacking Stroll's feedback, he said: "It hurts a lot. I think we miss him because some of my comments or my feelings with the car, we never know if it's just me in a new team and a new car, or it's just maybe an Aston Martin thing that Lance would spot.
"So brake pedal feeling, power steering...all these things I don't know if this is a legacy from the team, or is just new on this car. So yeah, we cannot do it without him, so I hope he can come back soon."
Intriguingly Alonso suggested that the AMR23 has changed so much that set-up information from the 2022 car is now "useless", as the car requires a different operating window.
"I think so far the car was responding well to the set-up changes," he said. "It was doing what we were expecting. The only thing is that the baseline set-up from last year is pretty much useless, because we operate in a very different window with this car.
"So that's very challenging now for the engineers, but they were very brave, very creative with different ideas in the last few days, and we found new ways to set up the car.
"We have very talented people in the team, so I trust them, and we will get more and more productive."
