Anderson's leg injury is described at this stage as "minor", but his unavailability would clearly be a major blow to England's hopes of closing out a 4-0 whitewash of India.
Twenty-eight-year-old Onions has not played a Test match since new year 2010, largely because of a long-term and once career-threatening back injury.
Tremlett was named in England's initial 13-man squad for the final match of the series, having missed both the second and third Tests at Trent Bridge and then Edgbaston - where his team-mates trounced India to take their country to the top of the International Cricket Council rankings for the first time.
But the Surrey fast bowler has succumbed again to the same back problem which ruled him out at Nottingham and then Birmingham.
Anderson has experienced tightness in his right quadriceps, and an England and Wales Cricket Board statement reported that his condition will "continue to be monitored over the next 48 hours".
National selector Geoff Miller explained both the reasons for Tremlett's unavailability, and Anderson's concerns.
"Unfortunately Chris Tremlett has failed a fitness test and won't be available for selection for the fourth npower Test, despite showing strong signs of recovery over the past few days," he said.
"Chris' absence, in conjunction with what appears to be a minor injury concern with Jimmy Anderson, has led to a call-up for Graham Onions as precautionary bowling cover.
"We are hopeful that Jimmy will overcome this niggle by Thursday, but more time is required before a decision on his availability can be made conclusively.
"Steven Finn is obviously in the squad and he is now joined by Graham Onions, who has been in good form for Durham since returning from a back injury at the start of the season."
Onions, who played three Ashes Tests to help England regain the urn in his debut summer in 2009, achieved greater fame as a number 11 batsman - twice blocking out the final over to salvage nail-biting draws on the 2009/10 tour of South Africa.
But his defiance in the second of those matches at Cape Town is his most recent act as an England player.
He was rested for the final Test of that series, as England lost at The Wanderers, and subsequently suffered an injury which ruled him out of the next campaign in Bangladesh.
Anderson has become England's unquestioned pace spearhead over the past two years, and has so far taken 18 India wickets in three matches this summer.
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Twenty-eight-year-old Onions has not played a Test match since new year 2010, largely because of a long-term and once career-threatening back injury.
Tremlett was named in England's initial 13-man squad for the final match of the series, having missed both the second and third Tests at Trent Bridge and then Edgbaston - where his team-mates trounced India to take their country to the top of the International Cricket Council rankings for the first time.
But the Surrey fast bowler has succumbed again to the same back problem which ruled him out at Nottingham and then Birmingham.
Anderson has experienced tightness in his right quadriceps, and an England and Wales Cricket Board statement reported that his condition will "continue to be monitored over the next 48 hours".
National selector Geoff Miller explained both the reasons for Tremlett's unavailability, and Anderson's concerns.
"Unfortunately Chris Tremlett has failed a fitness test and won't be available for selection for the fourth npower Test, despite showing strong signs of recovery over the past few days," he said.
"Chris' absence, in conjunction with what appears to be a minor injury concern with Jimmy Anderson, has led to a call-up for Graham Onions as precautionary bowling cover.
"We are hopeful that Jimmy will overcome this niggle by Thursday, but more time is required before a decision on his availability can be made conclusively.
"Steven Finn is obviously in the squad and he is now joined by Graham Onions, who has been in good form for Durham since returning from a back injury at the start of the season."
Onions, who played three Ashes Tests to help England regain the urn in his debut summer in 2009, achieved greater fame as a number 11 batsman - twice blocking out the final over to salvage nail-biting draws on the 2009/10 tour of South Africa.
But his defiance in the second of those matches at Cape Town is his most recent act as an England player.
He was rested for the final Test of that series, as England lost at The Wanderers, and subsequently suffered an injury which ruled him out of the next campaign in Bangladesh.
Anderson has become England's unquestioned pace spearhead over the past two years, and has so far taken 18 India wickets in three matches this summer.
Read more...
