"Perhaps I shouldn't have been - I suppose there must have been some unhappiness at the rate he felt he could do things - but I wasn't aware he was that unhappy until he came to tell me he wanted to leave.
"I thought he did a great job and I spent a great deal of last weekend trying to persuade him - I'd have dearly loved him to stay."
Triesman also rebuffed suggestions that the Premier League now holds more sway than the FA at football's top level.
Premier League boss Richard Scudamore had earlier highlighted "structural difficulty" at the FA, calling it an "aggregation of vested interests" while denying the Premier League had played any role in Watmore's departure, just nine months into the job.
"The Premier League run an incredibly successful league, and it does make them a powerful force, but the FA has a job to bring together the different interests and to get everyone to see the bigger interest overall," Triesman told 5 live's Sportsweek programme.
"Here we are with a group of people who represent everything from kids playing football in local parks and schools to people right at the top of the Premier League.
"Does it take work to bring them together? Yes, it does. The answer is, do the work.
"Does that mean a tough discussion on occasions? You know it does. But I'm not against having a tough discussion."
Dave and I are not on the same page
Lord Triesman on Wigan chairman Dave Whelan
The FA had already faced a bruising few months prior to Watmore's departure, beginning with the surprise resignation of Sir Dave Richards, the Premier League chairman, from England's 2018 World Cup bid team in November.
Karren Brady, who stood down from the same team earlier that month, told the BBC that the FA-led bid had been hit by "bickering, infighting and disruption".
Meanwhile, earlier this week Wigan chairman Dave Whelan called for a radical overhaul of the FA, suggesting the Premier League take over the administration of the England team.
"Dave and I are not on the same page," said Triesman. "I think Dave should re-read the Fifa statutes and he will find out we are responsible for the game overall in England, that's our mandate.
"I have no intention of seeing any of those rights given up and I think we are perfectly capable of doing it.
"If you look at the success of the England team at the moment under the general management of the FA and outstanding coach Fabio Capello, it's a bit hard to say we are getting it wrong.
"It could hardly be a better build-up to a World Cup in our recent experiences."
With that in mind, he denied the organisation's recent troubles called for a change of leadership.
"I think there's still a lot to do and I would hope to do it. Nobody has come to me and said they don't think I should do it.
"I intend first and foremost that we do very well at the 2010 World Cup in South Africa, and very well in our bid for the World Cup. I set myself positives, not negatives."
Alex Horne, previously the FA's chief operating officer, is Watmore's successor, a role he is expected to keep until the end of the year in an acting capacity.
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