The Republic of Ireland international was on the verge of joining Steve Bruce's side on transfer deadline day before the move fell through.
However, Clarke has now backed Long, who has scored eight Premier League goals in each of his past two seasons, to be involved in West Brom's challenge this term.
"Shane is a very, very important member of our squad. I'm delighted he’s here," Clarke told The Mirror.
On Long's proposed move to the KC Stadium, Clarke defended the club's stance and urged the former Reading striker to be open to a resolution.
"The club made a decision which was right for them – obviously I’m part of the club – but very quickly the bid collapsed," Clarke continued.
"Shane and his advisor need to sit down and talk with the club to try and get a resolution.
"Given contract talks had stalled for so long, it is possible that’s why the club originally accepted the bid."
Long has featured in all three of West Brom's Premier League games so far this season, with Clarke's side yet to score in the league.
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