The 19-year-old was not part of the 36-man squad that travelled to New Zealand for the club's pre-season tour on Thursday, as he continues to recover from injury.
He has, however, been told that he will be in and around De Zerbi's squad next season, with the club having no intention of selling him, reports the London Evening Standard.
Spurs consider Olusesi part of a small group of academy players they believe can challenge for first-team minutes either this season or in the future. Centre-back Jun'ai Byfield, also told he is part of De Zerbi's plans, and forward Luca Williams-Barnett are believed to be part of the same group, though it remains unclear whether Williams-Barnett will be involved with the first-team squad this season.
Olusesi was linked with a permanent move away from the club in January, with Hoffenheim and PSV Eindhoven both having bids rejected for the England youth international. Since then, he has continued to build his first-team experience, making his Premier League debut off the bench in Spurs' 1-1 draw away at Liverpool in March, before making his Champions League debut three days later as Spurs beat Atletico Madrid 3-2 in the second leg of their eventual 7-5 aggregate defeat to Diego Simeone's side.
A central midfielder by trade, Olusesi has been on Tottenham's books since progressing through the club's youth ranks, and was part of the side's Under-17 and Under-18 Premier League Cup double-winning squad before going full-time as a scholar.
His performances for the club's Under-21 side, including a run of five goals in five starts in Premier League 2 earlier this year, played a significant part in persuading the club to knock back approaches from Germany and the Netherlands during the winter window.
With De Zerbi now settling into pre-season, Olusesi's continued presence around the first team represents one of several encouraging signs for Tottenham's academy graduates, with the club increasingly keen to showcase a clearer route to regular senior football for its brightest prospects.