Watson was forced off the field mid-over by a groin problem on day four of the fourth Test at Chester-le-Street, though he did return to bat on the final day and has trained well in the build-up to the series finale.
Haddin said at a pre-match media conference: "He's been bowling today and came through that all right, and he did all the running unassisted which is a good sign.
"We'll see how he pulls up tomorrow but he's looking 100 per cent to go."
Watson's batting has not been impressive in this series, with only one half-century and an average of 27, though his miserly bowling has seen him concede less than two runs an over and provide an effective foil to the likes of Ryan Harris and Peter Siddle.
The pair are second and joint-third in the list of leading wicket-takers, with 20 and 17 respectively, and Haddin sees enough encouragement to raise hope of a consolation win after England opened up an unassailable 3-0 series lead in Durham.
"There's a lot of belief in the changing room that we can win this last Test," he said.
"We've been in a position over the Tests to put ourselves in a position to win, we just haven't been good enough in the big moments.
"England deserve to be in the position they are, 3-0 up, but it's up to us to build on the good things we've done and put it together over five days rather than just in patches."
Haddin is attaching no additional significance to the match, though, ahead of the return series Down Under this winter.
"I don't think it'll make much difference to what happens in the home series," he said.
"England have played better over this series but I don't think momentum will make much of a difference. We'd just like to get a win, we've played good enough cricket on this tour to deserve a win in a Test match."
That series will once again take place without Australia's exciting young paceman Pat Cummins.
The 20-year-old has still played just one Test, against South Africa in Johannesburg in 2011, because of his susceptibility to injury and a recurrence of a back problem looks set to rule him out of a second successive Ashes series.
A Cricket Australia statement read: "CA advises that Pat Cummins has suffered a recurrence of his lower back bone stress injury."
CA chief medical officer Justin Paoloni said: "Pat returned home early from the Australia A tour of Africa with some side/back soreness, and scans have shown a partial recurrence of his lower back bone stress injury suffered in October last year when he returned home from Champions League.
"He will be closely monitored to determine his return to the playing field, but (we) expect that he will miss most of the 2013-14 domestic cricket season."