During his decade at Everton, Osman has played 388 games and scored 54 goals for the club, although he insists there is more to come under Roberto Martinez.
Carragher, who was a boyhood Everton fan, has praised the veteran and congratulated him ahead of the testimonial.
Well deserved testimonial game for Leon Osman tomorrow. Very underrated player good footballer scores and creates goals.— Jamie Carragher (@Carra23) August 2, 2014
Despite his age, Osman played more games than any Everton midfielder last season (although not as many minutes).
|Gareth Barry||Man City||MF||3||4||32||2,849|
As Opta stats show, the 33-year-old scored three times and registered four assists over the course of a campaign that saw him take part in every single one of the Toffees' Premier League matches.
It is no wonder, then, that Carragher rates the midfielder - and that Osman himself sees a bright future in a blue shirt.
As well as their domestic ambitions this term, Martinez's men are also back in the Europa League.
"I'm not finished yet despite the testimonial,” he said recently. “I'd like to think I've got a few more seasons left in me at the top."