Douglas Ross had previously called on the Prime Minister to stand down over partygate, before backtracking due to the war in Ukraine.
Mr Ross has faced criticism for backtracking on his call for the Prime Minister to quit over parties in and around Downing Street during lockdown, citing the need for stability at the top of the UK Government due to the Russian invasion of Ukraine.
The Conservatives have struggled in the Scottish council elections, losing key seats and seeing their share of the vote drop by double-digits in a number of wards.
Speaking to the BBC from the election count in Moray, Mr Ross said: “It’s been a difficult night and the results coming in today are very disappointing.”
He highlighted gains in Moray and Aberdeenshire, but said: “In too many parts of Scotland, we’ve lost excellent candidates and councillors haven’t been re-elected because it seems many of our supporters decided to sit this one out, to protest and not cast their vote, and we’ve lost out as a result of that.”
When asked whether he believes Mr Johnson should lead the Conservatives into the next general election, Mr Ross said: “The Prime Minister simply can’t ignore the message that’s been sent from voters not just here in Scotland, but across the UK.
“The Conservatives lost Westminster Council last night – that’s a council that even in the peak Labour years under Tony Blair the party held on to – so there’s been a very strong message from the public to the Prime Minister and to the party.”