Alonso switched from his hard tyres to mediums as the first signs of a shower hit some areas of the track.
After the rain intensified and spread over the whole circuit, he quickly came in again for intermediates.
Alonso held onto his second place, but Krack insists that had the Spaniard made a single stop instead of two he still wouldn’t have beaten race winner Max Verstappen.
He stressed that the Silverstone outfit made the right call with the available information at the time.
"We need to look at the whole thing, how it went,” said Krack. “Obviously, you try to stay out as long as you can in such conditions when you do not really know what's going to happen.
“We did not anticipate so much rain, to be honest. So we thought that it would just be a short shower, and drying quickly because the track was very hot. Then normally, you would say, okay, we stay out one more, two or three more laps, but the tyres were worn already quite a lot.
“And we saw the temperatures going down. So that was a bit of a risk. When the car came in then with this information, we said, okay, let's fit the mediums. But then when the car left, shortly after we saw that it was really a lot of rain. And we had to come back.”
Source: Autosport