Fabio Capello toyed with the idea of picking Defoe for last Friday's encounter with Algeria, but after watching his team perform so poorly, was believed to have opted to unleash the Tottenham man on Slovenia, a match England must win to be certain of reaching the last 16.
Defoe has started just one competitive game for Capello - and lasted only one half of that, against Andorra in September 2008.
However, with 11 international goals to his name - and three in qualifying - Defoe is a more obvious threat to Slovenia than Emile Heskey and in theory, his extra pace would provide Wayne Rooney with more space to lift the gloom from his disappointing contribution so far.
Capello previously stated Matthew Upson would replace the suspended Jamie Carragher in central defence, where he was likely to become John Terry's third partner of the tournament, and fourth since Capello named his 30-man provisional squad given Rio Ferdinand had to fly home due to injury.
Terry has been the centre of attention for all the wrong reasons this week, but after apologising for his outburst on Sunday, there was never any question of Capello dropping the Chelsea captain.
James Milner was set to be England's third change, although having lasted only half an hour of the opening match against the United States before being hauled off, he would have been hoping to make a greater impact on his preferred right side.