The Health Secretary said he would prefer a “positive incentive as opposed to negative incentive” to encourage more young people to come forward and receive the vaccine.
He was speaking after figures from Public Health Scotland showed about 30% of 18 to 29-year-olds and 20% of 30 to 39-year-olds in Scotland have not had their first dose of coronavirus vaccine yet – despite every adult being offered a first appointment.
Concerns have been raised about the “alarming decline” in the number of Scots being vaccinated, as the programme rolls out to younger age groups.
Scottish Conservative MSP Murdo Fraser said: “If we’re going to defeat this virus we need to get the population vaccinated and 18 to 29-year-olds are the key group now.”
Speaking on BBC Radio Scotland’s Good Morning Scotland programme, he added: “What we’ve seen is quite an alarming decline in the numbers being vaccinated.
“On Monday the daily first doses of the vaccine hit a three-month low, only 2,483 people were vaccinated with a first dose on Monday, so we are really struggling to meet this key group.”
He said requiring a vaccine passport or proof of a negative coronavirus test to attend large-scale events like nightclubs or concerts is a “reasonable proposition”.
In England, full vaccination will be a condition of entry to clubs and other venues with large crowds from September and Boris Johnson has refused to rule out applying a similar rule for busy pubs.
Mr Yousaf told Good Morning Scotland he is “naturally, instinctively sceptical” about vaccine passports, saying groups representing young people have told him of fears these could “increase the inequality gap”.
But he added: “I wouldn’t rule it out entirely.
“We are making incredible success with our vaccination programme rollout, so I would like to look at what we can do to be proactive, as opposed to denying young people entry to a pub or a night club, I would much rather think about positive incentives.
“In extremis we might have to think about what else we might need to do in order to get more of the population vaccinated, so it protects us all.
“We wouldn’t rule it out entirely, but it’s certainly something I am instinctively quite sceptical about.”
Interim Scottish Liberal Democrat leader Alistair Carmichael insisted however that a vaccine passport scheme is “probably one of the most pointless and divisive exercises you can imagine”.
He said: “They will leave behind those who are not vaccinated for good reason or otherwise.
“If you have got everyone vaccinated then, frankly, you wonder whether it would be worth the expense and hassle.
“To threaten people in order to get the vaccine I think is the wrong approach altogether and I think it would be massively divisive.”