Portsmouth will check on Liam Lawrence ahead of the game after the winger sat out the Republic of Ireland's 1-1 draw with Slovakia on Tuesday night after suffering a leg injury against Russia four days earlier.
Hermann Hreidarsson could make his first appearance of the season, however.
The Iceland defender ruptured his Achilles against Tottenham last March but is on the comeback trail, having been involved with his international squad last week, and could be named on the bench.
Striker Danny Webber, who damaged knee ligaments in the same match as Hreidarsson, is another month away from returning.
Youngsters Tom Kilbey (knee) and Billy Goddard (shin) are still on the sidelines.
Ross Jenkins is Watford's only injury concern as they head to the south coast.
The midfielder has tweaked an ankle in training and is doubtful ahead of the Fratton Park clash, with his fitness being monitored closely.
Malky Mackay has an otherwise fully-fit squad at his disposal.
In-form striker Marvin Sordell had to be taken off at half-time of the win at Sheffield United last time out after taking a kick but the international break has allowed him time to recover and he is expected to lead the line.
The game represents the first meeting between the two clubs since 2007, when it was a Premier League fixture, with Watford running out 4-2 winners.