Jose Mourinho's side welcome the Premier League's bottom club to Old Trafford, hoping to spoil their rivals Manchester City's title celebrations with a win over the 'Baggies'.
The reverse fixture at the Hawthrones ended 2-1 in United's favour and Foster knows that Sunday's game will be a similarly tough test.
He told the club's official website: "We'll go there with our own game plan. We know, obviously, that United have got a lot of talent and a lot of pace and power up front".
The goalkeeper also spoke about the impact of caretaker manager Darren Moore, who stepped up after Alan Pardew was sacked following a run of eight straight defeats.
"Darren has been in the job for two weeks now and he has taken to it like a fish to water. He's massive on working as a team, getting confidence up and getting the lads enjoying their football.
"We've got to work on our shape when we haven't got the ball. When we have got the ball we've got to express ourselves like Mooro's big on us doing."
West Brom have 21 points and are currently bottom of the Premier League table, 12 points from safety with just five games remaining.