Midfielder Welsh elected to join League One counterparts Preston on Monday after turning down an offer to remain on the Wirral.
Offers remain on the table for playmaker Robinson and full-back Buchanan, and Moore is optimistic of receiving the answers he wants from the duo.
"Unfortunately we've lost John Welsh," he told Rovers' official website. "We put an offer in that we thought was a good offer for him but obviously he has got a better offer and gone to Preston.
"I wish him all the best there. He has been a great servant and since I've come in he's been fantastic. It leaves us a bit bare in that midfield area."
Moore added: "We've put the offer to Robbo and I don't think we're a million miles away from having that done, fingers crossed. I'll know soon on Buchs and I'm hopeful we'll get definite yeses on both of those two."