Buttler, left out of England's squad to face Pakistan in the first Test at Lord's next week, was injured keeping wicket in Lancashire's seven-wicket NatWest T20 Blast victory at home to Worcestershire but still opened his team's innings.
"X-rays later revealed he sustained a small stable fracture which will be managed conservatively," Lancashire said on their website (www.lccc.co.uk) on Sunday.
Worcestershire ran up a total of 198 which was overhauled with three wickets to spare as wicketkeeper Buttler scored Lancashire's fastest T20 half-century off 20 balls.
He was out in the sixth over by which time Lancashire had set a record for runs scored in T20 powerplay overs in England.
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His match-winning innings came three days after he had struck an unbeaten 73 in England's T20 win over Sri Lanka.
(Reporting by Rex Gowar; editing by Ken Ferris)
