United won two and lost two of their four games, with the victories coming away at Leicester and at home to Arsenal.
Ayoze Pérez scored in both of those games, as well as setting up Jonjo Shelvey's opener at the King Power Stadium and Matt Ritchie's winner against the Gunners, to earn a nomination for the monthly prize.
Dummett was shortlisted for March's award and has continued to produce consistently solid performances throughout April, while Diamé has enjoyed another excellent month.
The Senegalese midfielder won the award in January. Last month's winner was Kenedy while Martin Dúbravka won February's award. Skipper Jamaal Lascelles has received it on three occasions - in September, October and December. Mikel Merino was August's star man and Jacob Murphy won the award for November.
Fans can vote for their top performer - and be in with a chance of presenting the trophy to the winning player and winning tickets for this month's final Premier League fixture of the season at home to Chelsea.
There are also tickets for the match as runners-up prizes.
To vote, go to nufc.fun88.co.uk. Voting closes at midnight on Wednesday, 9th April.