The Blues boss was speaking after Saturday’s 1-1 draw with Tottenham Hotspur.
Lukaku sat out the encounter at Goodison Park after picking up a heel injury in the pre-season friendly defeat to Espanyol.
But Koeman confirmed that the 23-year-old Belgian striker would be ready to face the Baggies at the Hawthorns in a week’s time.
Koeman said: “He was already a doubt for today, but we had good hope that he was going to start. He will be ready for next week.
“The player likes to play and if he is okay, he will start.”
The Dutchman, however, was less optimistic over right-back Coleman‘s chances of featuring any time soon.
The Republic of Ireland international turned up to Goodison with his left foot in a protective boot, and played no part in the 2016/17 opener against Spurs.
And Koeman stated that the full back would be out of action for a while.
He added: “Seamus [Coleman] will be out for several weeks.”