The visitors are without loan midfielder Toby Collyer for the Vicarage Road clash as the Manchester United man misses out due to a hamstring injury.
Collyer impressed with a decent full home debut in the win against Preston before hobbling off after half-time. The likelihood is Jayson Molumby will return to the Baggies' midfield to face the Hornets.
The other likely change from Saturday's starting line-up is up front where Aune Heggebo is a good bet to replace Josh Maja.
Maja started just his second match back from a long-term injury absence on Saturday and as Albion manage the frontman's minutes the likelihood is Norway international Heggebo will rotate in.
The trip to Ipswich three days later offers Mason another opportunity to start Maja, if desired.
Albion's head coach may look into possible full-back changes with new summer signing Alfie Gilchrist still waiting for a first start at right-back. George Campbell has struggled at times out of position but was solid in Saturday's win over Preston.
Republic of Ireland's Jayson Molumby
Albion's Jayson Molumby, pictured away on international duty with Republic of Ireland earlier this month, is expected to return to the starting line-up. (PA)