The 27-year-old sustained the injury during Saturday's Premier League defeat to Aston Villa and has since withdrawn from the Spain squad for this month's international fixtures.
According to The Athletic, the right-back is expected to be sidelined for around a month because of the hamstring problem, ruling him out of Tottenham's trip to Manchester United on 10 October.
He could also miss the home match against Coventry City nine days later, on 19 October, depending on how his recovery progresses.
It is the latest in a lengthy run of muscular issues for Porro, who had only just returned to full training before Saturday's setback and was substituted early in the defeat at Villa Park.
The timing is particularly frustrating given his central role for Spain over the past year. Porro has made 24 appearances for the national team and was a key figure in this summer's World Cup triumph, scoring twice during the knockout stage, including the winning goal in the semi-final win over France.
At club level, he has made 156 appearances for Tottenham since joining the north London club, contributing 13 goals and 26 assists.
Porro signed a contract extension with Spurs earlier this year that runs until the summer of 2031, having previously attracted interest from other clubs following his rise to prominence as one of the Premier League's most productive attacking full-backs.
His absence adds to a difficult defensive injury list for Tottenham as they look to arrest a difficult start to the season under Roberto De Zerbi.
Porro's fitness has been a recurring theme this season. He had already missed two matches earlier in the campaign with a similar muscular complaint before being passed fit to face Aston Villa, only to be forced off inside the first 20 minutes.
For Spain, Porro's withdrawal opens the door for uncapped Sporting CP full-back Iván Fresneda to step up from the Under-21 squad and make his senior debut during the international window, according to reports in the Spanish press.
Porro's performances at the World Cup, where he was named in the tournament's team of the competition, had cemented his status as Luis de la Fuente's first-choice right-back, making his absence notable for the world champions as they open their Nations League campaign.