He singled out former manager Eddie Howe for special praise regarding his support through his 10-month Italian Football Federation betting suspension.
"A special mention to the gaffer, Eddie, who's been a real guiding figure and who always had my back throughout this journey," Tonali said.
Tottenham head coach Roberto De Zerbi, who took over in late March and avoided relegation, welcomed the reinforcement to his midfield unit.
"Given his qualities, there was a lot of interest in Sandro this summer," De Zerbi said.
"However, he was very clear in his desire to join Tottenham, and I know our fans will love what he brings to the team."
Club leadership expressed immense confidence in the Italian's ability to adjust to the intense demands of the squad's upcoming campaign.
"He has outstanding technical quality to go with real football intelligence, and has the character to thrive in a demanding, high-pressure environment," said Sporting Director Johan Lange.
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Financially, a BBC analysis noted that Tottenham remains compliant with the 85% squad-cost ratio rule because its prior wages and amortisation sat at 61%, complemented by annual commercial revenues surging to £277 million at its new stadium.
