Australia paceman Joe Mennie became the first player to be substituted out of a match in English cricket's County Championship under new concussion guidelines after suffering a blow to the head.
Mennie, whose lone Test appearance for Australia was against South Africa at Hobart in November 2016, received prolonged on-field treatment before walking off at New Road during the second day of a scheduled four.
Lancashire subsequently informed the match cricket liaison officer, Richard Ellison, of their intention to withdraw Mennie from the remainder of the fixture.
Former Kent and England swing bowler Ellison approved Lancashire's request to replace Mennie with Danny Lamb, who was travelling down from Manchester on Thursday.
Traditionally, substitutes in cricket have only been allowed to field, rather than bat or bowl.
But this season, the England and Wales Cricket Board has introduced a new concussion substitute rule which allows teams to name a like-for-like replacement, following medical examination and subject to the approval of the CLO.
Lancashire's concerns over Mennie, who has also played two one-day internationals for Australia, were particularly acute given he suffered a fractured skull while with the Sydney Sixers when hit on the head in the nets by a shot from Michael Lumb.
"Joe has taken quite a nasty impact on the side of the head just above the temple, quite a heavy blow," said Lancashire assistant coach Mark Chilton.
"That causes an immediate concern for everyone.
"At some point tonight (Thursday) he will undergo his concussion tests but at this minute it is just being considered as a head injury," Chilton added.
"He was conscious all the time but clearly not very well and pretty dazed by it and his head is sore. He is much better now and has shown signs of significant improvement.
"We took an early view because of the severity of the impact that we have to withdraw Joe from the game. There is very clear protocol to follow."
Mennie's injury capped a desperate day for Lancashire, who suffered a first-innings collapse before Worcestershire captain Daryl Mitchell made his second century of the match.
Meanwhile Guptill made 111 -- the first time a Worcestershire player had scored a Championship century on their debut since Phil Jaques against Surrey at The Oval in 2006.
Guptill hit 10 fours and four sixes in a blistering century before he was trapped lbw to Tom Bailey, with Mitchell going on to make 163 following his first-innings 118.
Earlier, Worcestershire seamer Ed Barnard managed the extraordinary feat of dismissing five batsmen for ducks during a return of five for 34 in 16 overs. At stumps, Worcestershire led by a commanding 478 runs with six wickets standing.
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