The left-back bruised his chest and ribs in a collision with Everton's Steve Watson in our last outing last week and was forced off after just 38 minutes. Thatcher said everything had 'tightened up' and he had struggled to breathe.
He has trained all week though and boss George Graham revealed after Sunday's session: "Ben's been out with us this morning, trained okay and will be fit to play West Ham."
The manager would not reveal whether or not the £5m man from Wimbledon would start though. Mauricio Taricco took his place and did well against Everton and Graham would only say: "The team will not be announced until Monday evening."
One player definitely out is midfielder Darren Anderton. He is expected to be sidelined for at least another three weeks after damaging his groin against Everton.
Stephen Clemence was a revelation after replacing Anderton - he created all three goals in the 3-2 win - and looks likely to start his first game of the season. Simon Davies may be promoted to the bench.
Meanwhile the news is good on three squad members yet to feature this season. Ledley King (broken foot), Chris Armstrong (groin) and Willem Korsten (hip surgery) are all back in full training. Graham added: "They've all done well but they are not ready yet. They've missed a lot of pre-season work and will all have to get match fit."
West Ham boss Harry Redknapp will be boosted by the return of Rio Ferdinand after a hip problem but long-term absentee Ian Pearce (broken leg) is still out. Igor Stimac is suspended after his red card against Leicester City and Darren Peacock, on loan from Blackburn, may make his debut.
Ben Thatcher is fit and available to face West Ham on Monday night.