The Blues captain has been plagued with fitness concerns during his career and lasted just 30 minutes in the club's 2-0 defeat to Everton on Sunday.
James suffered a hamstring injury in his side's 1-1 draw against Liverpool on the opening weekend of the Premier League season.
That problem saw him miss ten games, with Chelsea and James himself looking to manage his workload upon his return.
The Blues academy graduate, who chose not to join up with the England squad in November to avoid any setbacks, suffered a recurrence of the hamstring issue against Everton in front of a watching Gareth Southgate.
Speaking after the match, Pochettino said: "He felt something in his hamstring.
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"It's not so nice for him to suffer another injury. He is an important player."
It's another hammer blow for James, who has played just 363 Premier League minutes this season.
Reece James injury history
James is among Chelsea's best players whenever he is on the pitch but his fitness concerns represent a major problem.
The right-back has already had 17 periods of absence since coming into the west Londoners' first-team squad in 2019.
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His latest hamstring issue will likely sideline him again and add to the 90 games he has missed for Chelsea due to his various injury woes.
James has started 118 games across all competitions in his Blues career, with 81 of those coming in the Premier League.
However, he's been out of action due to injury for a total of 472 days.
His problems in the professional ranks started after an ankle injury while playing for England at the Toulon Tournament in June 2019.
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Since then, James has been sidelined with knee, thigh, and ankle problems, with his hamstrings a particular area of concern.
James also missed last year's World Cup in Qatar after suffering a knee injury in the build-up.
The latest hamstring injury he sustained at Goodison Park was the sixth the defender has been stricken within the past two years.
Incredibly, his longest run without fitness worries came during a season-long loan at Wigan in 2018/19 which still accounts for over 30 per cent of his career league starts.