The 32-year-old made his debut for the Baggies, following his summer switch from Manchester City, in their 1-0 win over Tottenham Hotspur, after being held out of their first four matches due to injury.
"We would have been taking a big risk with Joleon had we put him in before he was ready and I hope the fans understand that," Irvine told reporters.
"I keep trying to explain that we want to put people in the team but they have to be ready.We already had a setback with him in the pre-season friendly at [Nottingham] Forest but we felt he was ready this week.
"There were no niggles or aches after his work, everything was good and it was also the right opportunity to put him in."
The Baggies are 16th in the Premier League after five matches this season.