Red Devils boss Jose Mourinho was left counting the cost of the international break after Chris Smalling and Phil Jones sustained injuries on England duty to join Paul Pogba in the treatment room.
Leading scorer Zlatan Ibrahimovic and midfielder Ander Herrera are both suspended while fatigue may be an issue for Sergio Romero, Antonio Valencia and Marcos Rojo on their return from South America.
“If you look at United’s squad, in fact at all the top-six clubs, they have some fantastic players,” said Pulis.
“They’re able to compete in all major competitions this year because they’ve got strong squads, they haven’t just got 11 players. They’ve got 25 players, all internationals.
“If Jose gets a few injuries he can replace them with experienced internationals who have cost a lot of money, it’ll still be a top team.”
West Brom have exceeded expectations this campaign and head to Old Trafford eighth in the Premier League table, still with an outside chance of securing European football for next season.
Albion hold a slight edge over United since Sir Alex Ferguson’s departure as manager, winning on two of their last three visits to Old Trafford. Goals from from Morgan Amalfitano and Saido Berahino gave them a 2-1 victory in 2013 and Pulis earned a 1-0 success in 2015 when Chris Brunt’s free-kick deflected in off Jonas Olsson.
Despite West Brom’s good form and their recent record at Old Trafford, Pulis admits his side may need some similar luck to go their way if they are to get anything from the match.
“It’s lovely to have that record – two of the last three – but we’ll need a bit of fortune again. We’ll need to play to our maximum and Manchester United need to be off it a little bit,” said Pulis.
“Sometimes it goes your way, sometimes it doesn’t. We know we’re playing against a club that are financially miles in front of us but you get games like that in this league and you still can manage to win games if it goes right for you.”
Nacer Chadli is an injury concern for West Brom. The midfielder has returned from international duty with Belgium nursing a shoulder injury and he will be assessed along with striker Salomon Rondon, who only linked back up with the Albion squad on Friday following his World Cup qualifying exploits with Venezuela.
Matt Phillips continues to struggle with a hamstring injury and he is likely to remain out.