His comments came as Ipsos Mori released their final Holyrood poll with STV, putting the SNP’s constituency vote share at 50 per cent and their regional list vote share at 39 per cent.
The pollster said such a result would leave the SNP’s hopes of a majority “hanging in the balance”.
Their final poll, one of five published in the past 24 hours, could see the SNP return as many as 68 MSPs overall, but would require almost all of the marginal seats held by the Scottish Conservatives or Scottish Labour to change hands on polling day.
Douglas Ross’s party would likely finish in second place with 27 MSPs, with the poll estimating their support at 20 per cent – unchanged from Ipsos Mori’s previous poll – on the constituency vote with a strong showing on the regional list at 23 per cent (up two points).
Scottish Labour would be set for a disappointing day despite their constituency vote share of 22 per cent, a rise of four points, pushing them into second place in that part of the election.
Their regional list vote share of 18 per cent would likely leave them with just 19 MSPs, lower than their 2016 share.
The Scottish Greens’ regional vote share of 12 per cent would see them return a record 11 MSPs, with the Liberal Democrats (6 per cent constituency, 4 per cent regional list) set to return four MSPs.
Alba, Alex Salmond’s new party, is set to receive 2 per cent of the vote, according to this poll, which would leave them without any MSPs.
The poll also indicated the majority of voters had made their decision on who to vote for, but with 12 per cent stating they may still change their mind on the constituency ballot and 14 per cent stating the same on the regional list, many votes could still change hands.
Emily Gray, managing director of Ipsos MORI Scotland, said: “Whether there will be a SNP majority or not hangs in the balance.
“The election result may come down to how the parties perform in a small number of key marginal seats, as well as in the regional vote, which is likely to prove particularly important in determining which party is in second place.
"With a relatively high percentage of voters still saying they’ve not definitely decided, all the parties still have something to play for.”
Of those thinking of switching, one in five Scottish Labour voters (21 per cent) said they may change their mind.
A further 15 per cent of Labour voters said they may change their mind on the regional list, with 11 per cent of Conservatives and 9 per cent of SNP voters saying similar.
Three quarters (74 per cent) of SNP voters said they would back the party on both ballots, with 18 per cent stating they would back the Greens, 4 per cent Alba and 3 per cent Labour.