Benali was pleased to see the centre-forward given a chance in defeat at Arsenal.
He wrote for the Daily Echo: "Although they lost, I felt there was some cause for optimism. The opening goal, scored brilliantly by Cameron Archer, gave us some hope.
"Saints were ultimately undone by Arsenal's superior quality but I was pleased for Archer to get a goal and was quite surprised by what I saw from Paul Onuachu.
"He made a mark on the team and looks like he could be an option, even though he looked close to an exit this summer.
"I still think we need to see more from him before we can start asking for him to be a starter but his performance against Arsenal was a step in the right direction.
"Unfortunately, his opportunity was likely a direct result of Ross Stewart's latest injury. All of our hearts went out to him when he sat down, unable to continue at the Emirates.
"Stewart has had such a horrible time with injuries since joining Southampton. Last Saturday was his first start for the club, over a year on from his arrival.
We don't currently know the length of his injury but I'm keeping my fingers crossed that it's not another long-term blow."