Crystal Palace had a great run this season beating Chelsea, Arsenal and Liverpool and a win here will mean that they have beaten the historic big 4 teams.
Allardyce's men will face the Europa League finalists and the Eagles boss admits Jose Mourinho's focus could be on United's date with Ajax in Stockholm next Wednesday and not on the Palace clash.
The French duo are subject to interest from Crystal Palace according to an exclusive in The Sun, with Sam Allardyce having them on a list of summer targets.
Manchester United have won 16 of their 24 final day matches in the Premier League (D6 L2) - the most wins in the competition.
"That wouldn't have happened overseas".
'You only know them when you have them in good moments and bad moments.
"Because there is nothing riding on our fixture it is easy to change it".
"Their Premier League position is secured and it was all dependent on if they had that cash as to whether they made a move or not".
Tomkins, who returned to action against the Tigers after recovering from an ankle injury, will play a part in Palace's last game of the season.
Reacting, Allardyce said he will field his "fittest" players.
Christian Benteke has scored in his last two Premier League trips to Old Trafford, but both have ended in 1-3 defeats for his side. They don't want me to leave them out.
Jose Mourinho insists he will not make mistakes in his second season at Manchester United now that he knows the club better from the inside. "Everybody wants to go and play at Old Trafford and come off with a result, as hard as it might be".