The 29-year-old was hurt again during Tottenham's chastening opening-day defeat at Brentford, landing awkwardly on his shoulder just minutes after coming on as a 68th-minute substitute in the 3-0 loss.
An MRI scan has since confirmed a slight fracture, with Spurs expected to take a cautious approach to his recovery given his injury history.
Maddison's latest setback comes little over a year after he first suffered ACL damage at the end of last season. He attempted a comeback during pre-season but suffered a full rupture in the process, wiping out almost his entire 2025-26 campaign.
He did not return to action until May, making three appearances as Tottenham secured Premier League survival, and was also restricted during this summer's pre-season by a separate minor issue before working his way back into the matchday squad for the Brentford game.
Manager Roberto De Zerbi has moved to play down the severity of the new injury, describing it as a "small injury" in comments to reporters, and there is hope Maddison will not spend an extended period on the sidelines.
The England international was able to take part in limited training on Monday, and the expectation is that he could return before next month's extended international break, with Spurs' upcoming fixtures including Wednesday's Carabao Cup tie against Charlton Athletic and Saturday's Premier League visit of Newcastle United.
Tottenham have made a difficult start to the new season, sitting bottom of the Premier League table after their opening-weekend defeat, and will be keen to have Maddison back as soon as it is safe to do so given the creativity and experience he offers De Zerbi's midfield.
Maddison's absence adds further strain to a Tottenham squad already contending with a lengthy injury list heading into the new campaign, with the club having invested heavily in reshaping their attacking options over the summer.
His importance to De Zerbi's approach was underlined by his selection off the bench against Brentford despite limited match sharpness, a decision that reflected the head coach's determination to reintegrate him as soon as possible following such a damaging lost season.