The Canadian driver sustained a wrist injury – potentially even a break – following a bike accident whilst training in Spain a few days before the test.
That forced Aston Martin into promoting reserve driver and last year's F2 champion Felipe Drugovich to help Alonso put the AMR23 through its paces.
Drugovich spent two half-days behind the wheel and has been confirmed as Stroll's replacement this weekend if the 24-year-old is definitively ruled out.
Whilst Drugovich performed admirably, two-time F1 champion Alonso feels Stroll's feedback was missed.
“It (the test) hurt a lot (without Stroll),” said Alonso.
“We missed him because some of my comments and my feelings about the car, we never knew if it was just me in a new team and a new car, or is it an Aston Martin thing that Lance could have spotted.
“Brake-pedal feeling, power steering, all these things. I don't know if this is a legacy from the team or if it is just new to this car.
” So, yeah, we cannot do it without him so I hope he can come back very soon.”
Alonso backs Drugovich to step in and step up
Brazilian Drugovich completed 77 laps of running on the final day of the test on Saturday, only three fewer than Alonso, and was six-tenths of a second slower.
Despite only one day in total testing the new car for the 22-year-old, Alonso has no doubt Drugovich will step up to the plate this weekend if required.
“Even myself, I feel I'm lacking laps and kilometres, so I cannot imagine for Felipe how difficult and challenging it is,” assessed Alonso.
“But he's a super-talented driver and he has adapted very well. We saw (on Saturday) he was immediately on the pace and on a good run plan.
“So if he has to race I think he will do a very good job because he has a talent.”