Scottish Conservative leader Douglas Ross admitted he was "not sure" if Mr Johnson would travel north ahead of the May 6 poll.
He said he had "previously expected" the UK party leader to come to Scotland, but said the coronavirus pandemic, and restrictions imposed as a result, made it a "very different" type of campaign.
The Prime Minister visited Scotland at the end of January, when coronavirus levels were much higher and a "stay at home" order was in place, with people told only to make necessary trips.
Asked if Mr Johnson would be campaigning in Scotland ahead of the election, Mr Ross said: "I am not sure he is going to come up."
Speaking on BBC Radio Scotland's Good Morning Scotland programme, he said: "I had previously expected him to come up. Clearly as we continue to tackle the Covid-19 pandemic this whole election is very different.
"Clearly it is a different election than any of us have experienced before."
With four weeks to go until polling day, he said "we will have to see what happens".
Mr Ross added: "Last time he was up here he was supporting our vaccinators, he was looking at how we are getting the vaccine rolled out across Scotland, the successful scheme across all of the United Kingdom.
"Now we are in an election campaign it is very different. He wouldn't be coming up to speak to a big meeting or doing a massive visit as previous leaders have done.
"It is very different. We have seen all the party leaders in Scotland having to tackle this election in a very different way because we are still living under significant restrictions."
He said: "The Prime Minister is fully in touch with what we are doing here, but he understands it's my campaign as leader of the Scottish Conservatives, it is our manifesto, he is absolutely behind what we are doing here in Scotland, but he knows our fight is as Scottish Conservatives and he is backing that as Prime Minister of the United Kingdom."
SNP depute leader Keith Brown said: "The fact Boris Johnson is being kept away from Scotland in this campaign, despite previously pledging to visit, shows the Tories know just how unpopular he is with Scottish voters.
"We were told just last week by Ruth Davidson that she was 'ringing the alarm bell' for the Union, but Boris Johnson must not be hearing it as he cannot even bring himself to come to Scotland to make the case."
Mr Brown added: "Running scared of the people of Scotland is becoming a theme within the Tories, with Baroness Davidson herself running away from accountability and scrutiny as she heads off to take up her £300-a-day job in the unelected House of Lords."
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