The 26-year-old loanee scored an impressive hat-trick in the 4-1 win over Motherwell on Sunday afternoon, and has now hit six goals in his last five outings.
The Norway international cost parent club Southampton around £16 million when he joined from FC Basel in 2018, and Ferguson has suggested that his recent purple patch is beginning to justify that hefty price tag.
Elyounoussi came in for criticism last week when he was spotted using his mobile phone in the stands after being taken off during the Bhoys’ Europa League defeat to Sparta Prague.
But the former Rangers midfielder has praised the player for his response to that incident, as well as singling out teammate Tom Rogic for his influential display at the weekend.
Speaking on the Go Radio Football Show, the pundit said: “It’s the big question mark that’s always been over him, but certainly in the last couple of weeks, he’s shown why Southampton did go and pay that £16 million.
"Again, it was a big call from Neil Lennon. He put him in on Sunday, and there were a lot of people chatting about him being on his mobile, but Neil Lennon put him in the team and he got a hat-trick.
"I thought he was outstanding, but the guy that stood out for me was Rogic. I thought he was the difference.
"That first 45 minutes he was just stringing things together for Celtic. He was immense in there.”