Watmore is ahead of schedule as he recovers from the ankle injury suffered at Wycombe Wanderers in March.
Sunderland had initially expected that problem to end his season but their play-off particpation and the players impressive recovery could see him involved in some capacity at Fratton Park.
“Hes obviously ahead of schedule and looks good and bright and positive in training, so hes probably forced his way into the reckoning much more than we would have imagined.
Ross had hoped last week that Watmore would continue to improve and remarked that depending on how the first leg panned out, he could be tempted to use the 25-year-old.
Chris Maguires second-half volley is the only thing that separates the two sides at the midway point, resulting in Portsmouth needing to score twice without reply from the Black Cats in order to book their place in the Wembley final.
The popular forward would offer a fresh attacking option if Sunderland do need a goal at any stage, but his ability to stretch the game and play on the counter could also come in handy should his side have to absorb and release any pressure late on.
And bearing in mind the second leg is in Pompeys back yard, Ross is expecting nothing less than a cauldron of hostile noise to greet him and his players tomorrow evening.
“We did a little bit of big pitch stuff on Sunday with the players who hadnt been involved on Saturday night, and he looked good again.
Jack Ross has provided a fitness update over attacking duo Aiden McGeady and Duncan Watmore ahead of Thursdays Sky Bet League One Play-off second leg at Portsmouth.
Whoever is running the club – and Donald wants to remain part of any future regime – Ross’s position will be strengthened if Sunderland defend their lead against Pompey and then win at Wembley later this month.
Jack Ross issues promising injury update ahead of crunch clash with Portsmouth
McGeady was forced to withdraw from the first leg warm-up on Saturday after hed initially been named in the starting XI to face Portsmouth.
Watmore, meanwhile, is back in training and close to full fitness after enduring a spell on the sidelines with an ankle ligaments injury picked up at Wycombe Wanderers in March.
Sunderland travel to Fratton Park on Thursday evening (KO 7.45pm) with a 1-0 lead thanks to Chris Maguires stunning volley, with ONien confident the Black Cats will book their place in the League One play-off Wembley final on May 26.
Speaking at Tuesdays press conference, Ross provided the latest on the pair as Sunderland look to make the most of their first leg advantage and seal their place in the final at Wembley.
The battle is far from over – ONien
He continued: Duncan has trained well and with that in mind hes probably put himself into my thoughts for Thursday.