Duff was widely tipped to quit the club after putting his house on the market but Martin says it would take a big club to tempt him away from Newcastle
Martin is coaching the player in Portugal with the Republic of Ireland.
Martin: "He looks great in training over here and there are two games coming up for him to get his teeth into.
Zico Backs Toon Winger To Stay!
"We've got a game against Serbia at Croke Park on Saturday and then Colombia at Craven Cottage. So he'll be involved there.
"He hasn't been involved at Newcastle but, knowing Damien, he won't sit back.
"He's a lad who will work hard and try to get his form going.
"I think his plan is to stick in at Newcastle. Whether he plays or not is solely down to Kevin Keegan, and up until the last game he didn't play too much.
"That was down to the formation in which Mark Viduka, Oba Martins and Michael Owen were the front three which doesn't leave much on the table if you are a winger, so it's not just Damien.
"Any player who is a winger will suffer in that situation.
"Personally I don't think Newcastle will play like that week in, week out.
"There'll be competition for places and Damien can concentrate on getting a good run."