Graham Westley took over at Peterborough in September last year and was sacked on Sunday after Saturday's 2-0 home defeat to Scunthorpe.
Peterborough are currently 14th in the table after their fourth defeat in five League One matches and only two games remaining this season.
The club's statement read, "The club would like to thank Graham for his efforts.
"Grant McCann will take charge of the remaining two Sky Bet League One fixtures. Chairman Darragh MacAnthony will take time to speak to prospective candidates for the vacant manager position."