Yousaf resigned as first minister in April 2024, about 13 months after winning the leadership contest.
He said he did not question the spending at the time, noting he was serving as health secretary during the Covid pandemic for part of the period.
He said his successor, John Swinney, was the right man to lead the SNP through the current period.
Swinney has repeatedly denied the need for a public inquiry, describing the police investigation as sufficient.
However he told MSPs on Thursday that the SNP may have claimed back tax on Murrell’s illicit purchases.
The SNP leader said his party had written to HMRC over the matter.
Yousaf said Murrell’s stigma continues to follow the party.
He said: “It was a very difficult time for the party, it kept coming up on the doorstep.
“I think the party is still finding it very difficult.”