West Brom have sacked Nicolas Anelka citing "gross misconduct" after the striker claimed on Twitter he had quit the club.
Mauricio Pochettino expects to be at Southampton next season and is looking forward to working with chairman Ralph Krueger.
The Iron lost 2-1 to their local rivals in the first-round replay on Tuesday night and Laws has paid the price.
The 52-year-old, who first took charge of the club in 1997, returned to Glanford Park for a third spell as manager in October 2012 but could not prevent his side from dropping to the fourth tier in his first season back at the helm.
United sit 12th in the Sky Bet League Two table, two points off the play-off places but are without a win in their last five matches.
Scunthorpe released the following statement on their official Twitter account: "Scunthorpe United can confirm that they have terminated the contract of manager Brian Laws with immediate effect.
"A further statement will be made later in the day."