Steve Clarke lost his job as Baggies boss in the wake of their 1-0 defeat to Cardiff on Saturday, their fourth in the row in the Premier League.
That defeat leaves West Brom in 16th place in the table, just two points above the drop zone.
Games against Hull City, Tottenham, West Ham and Newcastle await them over the Christmas period and Reid has urged his team-mates to "dig in" to ensure their survival.
"We can't feel sorry for ourselves. We have the biggest few fixtures of our campaign - this period will define our season," he said.
"(With) the form we're in at the minute we need to dig in.
"Make no mistake about it, we are in it. We are in a relegation fight with other clubs and we can't forget that."
Joint-assistant head coach Keith Downing will take charge of the team for the visit of Hull on Saturday as the West Brom board consider candidates to take over on a permanent basis.
But Reid is confident the right candidate will be appointed as the club looks to retain their top-flight status having returned to the Premier League in 2010.
"The board have got it right with the last few appointments," he added.
"Roberto Di Matteo got it and took us on to promotion (to the Premier League in 2010).
"Roy (Hodgson) took us to another level of mid-table safety and Steve Clarke gave us our best-ever Premier League finish (eighth, last season).
"It will need to be a top-class coach, which is something we've had over the last couple of years.
"I wouldn't have thought someone will come in and break it away because what we've been doing the last few years has been the right way.
"The board will hope the new man gives the players a lift and gets us some results."