They were preparing for the home tie when they decided to leave the temporary building they were training in only for it to blow down later in high winds yesterday.
De Boer was worried by the strength of the gale and decided to take his players out of the inflatable structure.
The coach said: "This was a good choice to move. A storm is the worst circumstance in which to train.
"We found the risk too great."
The club confirmed that nobody was in the building at the time it blew over.