Stock, sidelined following ankle surgery, was an unused substitute at Coventry last time out, but manager Sean O'Driscoll may be tempted to hand him his comeback following Simon Gillett's return to Southampton.
Gillett is currently mulling over a permanent switch to Doncaster following the end of his loan spell.
Another midfielder, Martin Woods, returned to full training this week after a groin problem.
Woods last appeared in the home win over Sheffield Wednesday in early December and has missed the last three matches.
Defender Adam Lockwood has still not completely recovered from a foot injury that has kept him out for three months, while young striker Waide Fairhurst is nursing damaged ankle ligaments. Long-term absentee Steve Brooker (Achilles) is edging his way back to full fitness.
Heidar Helguson is back in the Watford squad for the trip.
The popular Iceland striker has rejoined the Hornets for a third spell on loan from QPR and is likely to go straight into the starting line-up.
Teenage midfielder Ross Jenkins could also start after returning as a half-time substitute during the 5-0 FA Cup defeat at Chelsea.
Jenkins had been sidelined for two and a half months following a back operation.
Boss Malky Mackay is close to completing the signing of Scotland Under-21 midfielder Stephen McGinn from St Mirren, but he is not expected to link up with his new team-mates until Monday.
Slovenian defender Jure Travner has joined Norwegian side FK Haugesund on trial.
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