Relegation rivals Northampton are also playing in an early kick off against London Wasps as the race to avoid bottom spot continues to heat up.
But Brain insists his team will only have the clash in Reading on their minds and not the implication of results elsewhere.
"We're in a similar position to when we went to Gloucester and Northampton kicked off early and won, but I don't think that had an impact on the performance of our guys at all," he said.
"Yes, we will know the result between Wasps and Northampton, that is unavoidable, by the time we go out to warm-up we will know the score.
"The players know that an opportunity could present itself possibly on Sunday afternoon, but we have got to be in the right frame of mind to take it.
"I am confident we can perform well on the weekend and if we do that we will be in with a real chance of winning the game. We are treating this as a must-win game."
After a run of five successive wins in the Guinness Premiership, Irish have slipped to back to back defeats to Saracens and Harlequins.
Worcester also secured a 20-15 the last time the two teams met at the Madejski in September 2005.
But Brain has warned that the hosts will be fired-up to secure a final home win.
He said: "It is always tough to get an away win and they will be focussed on winning their last game at home, they will want to put on a good show in front of their support.
"We have got to make sure we look after the ball, make sure we defend well against what can be a potent attacking team. The key thing is the more we look after the ball, the less time we spend defending the more dangerous we look with people running with it."
Worcester Warriors team to face London Irish:
01 Tony Windo, 02 Aleki Lutui, 03 Chris Horsman, 04 Will Bowley, 05 Richard Blaze, 06 Drew Hickey, 07 Pat Sanderson (c), 08 Kai Horstmann, 09 Matt Powell, 10 James Brown, 11 Thinus Delport, 12 Gary Trueman, 13 Dale Rasmussen, 14 Lee Best, 15 Shane Drahm
Replacements: 16 Darren Morris, 17 Chris Fortey, 18 Tevita Taumoepeau, 19 Phil Murphy, 20 Gavin Quinnell, 21 Nick Runciman, 22 Mark Tucker