The 31-year-old Worcestershire spinner was struck by a ball from Courtney Walsh during the concluding overs. It was thought at first he had suffered only bruising but an X-ray revealed a crack in his right index finger.
Illingworth is unlikely to resume his innings this morning, which effectively leaves England five down, but there is a consolation in that the damage is not to his bowling hand. Selected as one of two front-line spinners in England's attack, the slow left-armer is expected to play a key role on a slow pitch prepared to help the spinners.
It is the second break Illingworth has suffered in the current series, having had his left knuckle fractured in the third Test at Edgbaston, which caused him to miss the Old Trafford Test.
Team spokesman Richard Little said: "He has been very unlucky. In his whole career he had only suffered one hand injury, a broken thumb, and now he has had cracks in each of his last two Tests."
Mike Atherton played only after undergoing a morning fitness test on his chronic back problem, which had flared up on Tuesday and required him to undergo electrotherapy and special swimming exercises. Graeme Hick, chosen ahead of Alan Wells, was named after he passed a check-up on a shoulder strain.
The captain's century was his third on the Trent Bridge ground in Test matches and brought particular gratification to retiring groundsman Ron Allsopp, 65 next month, who was determined his last Test match pitch would see English batsmen scoring runs and English spin bowlers taking wickets.
"In the circumstances, I'm quite pleased with the way it is playing," Allsopp said. "I don't see any problem, within reason, with preparing pitches that suit our strengths and the main objective has been achieved in that the ball has not been flying at anyone's throat."Reuse content