Although the Hammers boss would not be pressured into criticising individuals publicly, he was clearly dismayed by his side's second half performance.
He said: "The four goals we conceded in the second half were absolute shockers, it was diabolical defending.
"For a team that has kept three clean sheets in its previous five games, it was very poor and we let the fans down.
"But I'm not going to criticise individuals here. What was said in the dressing-room will remain there and we've got to stay tight as a team.
"We'll have a good chat on Monday or Tuesday after I have looked at the video of today, which won't make good viewing."
The manager admitted it was a Jekyll and Hyde performance by his team, who had swept aside in-form Newcastle United at Upton Park just six days earlier.
Roeder also confirmed that young striker Jermain Defoe was absent due to a thigh strain that will prevent him from joining up with the England under-21 squad next week.