Professor Jason Leitch said apps that automatically trace contacts need to be used by around 60% of the population to be effective in public health terms.
He was asked about the Scottish Government's test, trace, isolate (TTI) strategy on BBC Radio Scotland's Good Morning Scotland programme on Tuesday.
On Monday, Nicola Sturgeon set out plans to recruit 2,000 contact tracers to enable the strategy to go ahead, with a daily testing capacity of 15,500 needed.
The UK Government is currently trialling the use of a Bluetooth-based app that can track and trace contacts between users - alerting people if someone they interacted with has displayed symptoms or tested positive for the virus.
Prof Leitch said: "It's being tested later this week in the Isle of Wight and Scotland is involved in its development.
"But we want to be sure, as you heard the First Minister say yesterday, of the security of that app, of its use - that it will work - before we layer it on top of what we're already planning
"We don't want to build from it, we want to use it as an additional element."
He said such apps could not simply be bought off the shelf on an international level, saying "they vary hugely in their ability to work".
Prof Leitch added: "Even in some of the countries that have had this for a while, the numbers of people who download it are 15%, 12%.
"You need high 60% or more for it to really help you at a public health and population level."
Asked if he or the Scottish Government would recommend the Bluetooth app, Prof Leitch said: "I'll download it myself once I'm confident that it works, the security is good and it feeds into our Scottish systems
"We don't know that yet. Nobody can know that yet because it's just been developed."
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