Reading winger Jimmy Kebe, who has been sidelined for five matches with a knee problem, could return to the squad, but Brynjar Gunnarsson is out.
Club captain Ivar Ingimarsson has suffered a minor setback in his recovery from a hamstring problem and is still unavailable.
After an excellent run of results, Watford have been struggling of late and have slipped from third to 13th in the table after taking only four points from the last possible 18.
They have lost their last two matches - both 3-2 - but, curiously, have also replaced second-placed Queens Park Rangers as the second highest scorers in the Championship behind leaders Cardiff.
The Hornets have netted an impressive 31 goals this season, only two less than Cardiff, but ninth-placed Reading themselves pose a real threat - especially late in games.
Reading, who have drawn their last two matches, have scored 10 goals in the final 15 minutes of matches this season - more than any other team in the division.
• Five of the last eight matches between these clubs have finished in a draw.
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• Watford's 3-0 win against Reading at Vicarage Road last season was their first home victory over the Royals in five attempts.
• Watford are averaging a goal every six attempts.
• They have committed 153 fouls this season - fewer than any other Championship side.
• Adrian Mariappa is set to make his 150th league appearance for the club.
• A draw would be Reading's 100th away from home in the second tier, while a win would take the club's total number of points at that level to 1,000.
• They are yet to lose a game this season after scoring first, and are yet to win after conceding the opener.
• Jobi McAnuff, a former Watford player, is in line for his 400th career appearance.
Source: BBC Sport