Openreach said the problem was discovered after power was restored to the island following Storm Amy, which caused huge disruption across Scotland last week.
“Following widespread power outages across the Hebrides, caused by Storm Amy, we’ve identified some damage to our subsea cable between Tiree and Tobermory,” a spokesperson for the company told The National.
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“This became apparent once power was restored and means homes on Tiree are currently without broadband.”
Engineers are due to arrive on the first ferry to the island on Thursday morning.
They will install a temporary connection while permanent repairs are planned.
“In the meantime, we appreciate the patience and understanding of everyone affected,” the company added.
Storm Amy brought strong winds and heavy rain to parts of Scotland earlier this week, leaving thousands without power and disrupting ferry services.