The striker left the club's training ground on Thursday after being given compassionate leave, granted after he learned of the sudden death of his agent.
"Nicolas lost a close friend and an agent over the weekend - he died suddenly," Clarke told the press. "Nicolas went to Richard [Garlick, technical director] on Thursday and indicated that he wasn't in a good place.
"I went in and had a very brief chat with him and he wasn't in a good place so the club have decided just to give him a bit of time to go away and think about it and get himself in a better place for the future.
|6/5||Everton are 6/5 with Bet365 to keep a clean sheet against West Brom
"I'm not going to deny that he used that word [retirement] in the conversations we had with him but we've given him time to go away and think about it and I don't think we could do any more in the circumstances as they were.
"He hasn't trained this week [because of a knock]. I was preparing the team for Everton without him."
One player who Clarke will have available for the trip to Goodison Park is new loan signing Scott Sinclair. The Baggies completed a season-long deal for the 24-year-old on Thursday and the Scot is now eager to see him in action.
"We needed width in team and he can score," the West Brom boss added. "He's hungry and desperate to play this weekend. It's a big year for him.
"We would like another wide player if possible; we have been under-active compared to others [in the transfer window]. I'm hoping we will be busy."