Defoe, who scored on his debut for Portsmouth on Saturday following his move from Tottenham on Thursday, was drafted in after Agbonlahor limped off during Aston Villa's Barclays Premier League defeat to Fulham on Sunday.
It is understood England manager Fabio Capello has stressed to Defoe the fact he has moved clubs and is now a first-choice striker puts him right into his reckoning for international consideration.
Defoe had not been in Capello's initial 30-man provisional squad announced last week, but he was a Tottenham player at the time and his change of club has pushed him up the pecking order in Capello's mind, though he would also have been aided by the loss of Emile Heskey to injury.
A Football Association spokesman confirmed the change to the squad following the desperately disappointing news for Agbonlahor who had been in line to make his England debut.
The FA spokesman explained: "We have called Jermain Defoe into the squad after Gabriel Agbonlahor was ruled out."
The 21-year-old Villa striker will not be required to join up with the squad ahead of Wednesday's friendly at Wembley.