Malcolm Turnbull could be compelled to give evidence to a Senate committee about a decision to give more than $440 million to a private sector backed Great Barrier Reef charity.

Committee chairman Peter Whish-Wilson said the former prime minister could be summoned when he resigns his seat on Friday. Senate committees can't force lower house MPs to front hearings.

Senator Whish-Wilson wants to question Mr Turnbull about an April 9 meeting with Great Barrier Reef Foundation chair John Schubert and former environment minister, Josh Frydenberg, when funding for the group was discussed.

"I'll be seeking to work with the committee to invite him as a witness and compel him if we have to," the Greens senator told The Australian on Wednesday.

"He is the one person who can answer our questions that haven't been answered, and get to the bottom of this."

The $444 million grant given to the Great Barrier Reef Foundation has been criticised because it was settled without a competitive tender process, with federal Labor describing it as an "extraordinary abuse of process".