Professor Luke O'Neill says asking people to wear face coverings while on busy Dublin streets is "not an unreasonable thing to suggest".
It comes after Dr Jack Lambert, a consultant in infectious diseases, says masks should be warn on the streets of the capital - and not just when you are in shops or on public transport.
The number of confirmed COVID-19 cases in Dublin continues to grow, with 133 reported there on Saturday and 68 on Sunday.
Prof O'Neill, professor of biochemistry at Trinity College Dublin, told Pat Kenny it could be the way to go.
"In Asia that happens, Pat, if you look at a street in Tokyo and there's crowds they're all wearing masks.
"That's simply to do with you can't keep the distance in that situation.
"Remember: if you stay two metres away that's really good, and outdoors is even better.
"But if you get within a few inches of someone that you're in a crowded street it would be wise to put your mask on.
"In fact some countries recommended that [you] keep your mask handy - if you find yourself in a crowded place outdoors, pop the mask on - being careful of course not to touch it too much.
"But that's not an unreasonable thing to suggest".
On the re-opening of pubs, Prof O'Neill said: "They've got to make sure, Pat, they're following the guidelines there.
"We have great sympathy for publicans at this stage, let's face it, and Ireland's been especially stringent as we know.
"That seems to have been because they claim we don't behave ourselves like someone in a French pub does - whether that's true or not I don't know.
"But certainly if they adopt the guidelines that are going to be stringently suggested then they should be OK.
"They're still risky places though, remember, and as I said to someone last week it's like God's having a joke on the Irish: pubs are the perfect place for this virus to spread, unless you mitigate.
"And they are going to have all these mitigating rules I guess.
"I think we have to open them, lets face it, for all kinds of social reasons - especially rural pubs, by the way, but they should have opened anyway cause the risk would be lower there".
