The 30-year-old forward, who made the move to The Hawthorns from Sunderland last year, played a key part for his side against Liverpool in their last game, surging forward to win the penalty which Saido Berahino tucked away.
The Baggies went on to lose the match 2-1, although Irvine was pleased with what he saw from Sessegnon in the second 45 minutes in particular.
"He was one who we certainly saw a difference in from first half to second at Liverpool," he told the Birmingham Mail. "I thought there was a huge difference. At half time I was thinking he was one of the players I might have to take off.
"Within a short time of the second half starting I was thinking 'There's no way he's coming off' because he was being effective. He is the type of player who is only being effective when he's playing with confidence and self-belief because what he does is hard.
"The players that run with the ball and go past people have the hardest job and I'm not talking as a member of the wingers' union here. He's got to believe in himself and be somebody who wants the ball and thinks 'I can do this'."
West Brom return to league action on Monday night when they host Manchester United.