The 33-year-old was one of the reasons why the Black Cats retained their top-flight status, and the all-time record Premier League goalscorer echoed that.
Defoe scored 18 goals last season, 15 in the league, as he managed to keep Sunderland in the top-flight for the tenth-straight season.
Overlooked for place at the Euro’s
However, the forward wasn’t considered for a place in Roy Hodgson’s preliminary 26-man squad, which was cut by three after the final submission Tuesday gone.
Shearer was full of praise for the Black Cats’ forward after the impact he had for Sam Allardyce’s side, and he believes that Defoe and Newcastle’s Andros Townsend are unfortunate not to be in the squad.
“When you look at it really, both of them can count themselves unlucky,” he told the Sunderland Echo.
Shearer feels that Townsend was “one of the few positives” for the Magpies in the final months of the season, while Defoe’s goals was “one of the main reasons” why Sunderland stayed in the Premier League.
Shearer hoping Three Lions can emulate Foxes success
Shearer understands why Defoe was left out with all the youngsters in the squad, but the former England man also hopes that the Three Lions can take inspiration from Leicester City’s title-winning season.
Only one man from that title-winning side is in the squad, Jamie Vardy, after Hodgson opted to leave out Danny Drinkwater.
Shearer added: “I don’t think we can win it, but you never know – Leicester won the Premier League so anything’s possible.
“I’m hoping we can get to at least a semi-final.”