The striker's current deal expires in June.
Clarke said: "It's not for me to put a time scale on it. My job is to coach the team, but the people who are working on the contract tell me it's close.
"He has been terrific for us this season.
"I've spoken a lot about Saido. He had a good pre-season, he forced himself into the front line for us, he's scored goals, he trains and plays with enthusiasm - he's been a breath of fresh air, he's been good."
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