Peel, who has won 76 caps and was a Test Lion six years ago, is set to miss out on a place in Wales coach Gatland's 30-man World Cup squad to be announced next Monday.
He has played no part in Wales' tournament warm-up games this month, with Gatland ready to select Mike Phillips, Tavis Knoyle and Lloyd Williams as his number nines for the New Zealand expedition.
Premiership Rugby's player release criteria meant Peel could not train with Wales before August 4, a factor Gatland conceded had gone against him.
Gatland also said earlier this week that Sale had told the Wales management Peel was unfit, although that claim was subsequently rejected by Sharks' executive director of sport Steve Diamond.
"Dwayne did have a finger injury but he has not missed one single training session since June 6," Diamond said on Tuesday.
"He was declared to go into contact last month and it is not right for Wales to say he is injured.
"The Wales management have not discussed Dwayne or any of our other Welsh players in the six months I have been back at the club."
Gatland said today he had not been in contact with Diamond, but he had spoken to current Sale coach Tony Hanks "a number of times".
"The day-to-day coaching is done by Tony Hanks, and I have spoken to him a number of times about his players, including Dwayne and Andy Powell, and I met him in London last week," said Gatland.
"I was disappointed to read Steve Diamond's comments.
"We received an email from the Sale physiotherapist on August 8 which said Dwayne had a problem with his hip and was not taking part in contact training. We used that information to make the decision not to include him.
"The way we have been training in the last couple of months has been very physical, and because Dwayne was not available to train with us in July there was always going to be a question mark over his fitness.
"That does not mean that if there is an injury to an experienced player like Mike Phillips that we would not go to Dwayne."
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