The Baggies accepted an offer from Hull City for the Republic of Ireland striker on deadline day but the move fell through when Clarke personally intervened to ensure that Long was not sold.
Albion signed attackers Stephane Sessegnon and Victor Anichebe before the summer transfer window closed, placing doubt on the former Reading man's future, but Clarke says Long is very much a key part of his playing group.
"Shane Long is a very, very important member of our squad," he told the club's official website.
"I've always said that since I came in. I'm delighted he's here.
"I spoke to him on deadline day but not since because he's been with his country and I have to be respectful to them.
"He has had to concentrate on what he was doing with Ireland.
"We will sit down to have a chat and we'll go forward from there. Shane's got a big contribution to make this season."