And that could mean England will have to find themselves another opener and a new wicketkeeper to face West Indies at Old Trafford next Thursday.
"I'm not ruling anything out at the moment," said Stewart, who indicated earlier this week that he thought he would be fit to bat in the Test, but not keep wicket.
"The finger isn't right yet, but there is still a week to go. I will speak to Ray Illingworth and Mike Atherton before their Saturday night selection meeting and bring them up to date."
Illingworth, the chairman of selectors, believes it will be all or nothing for Stewart at Old Trafford, however. "I haven't spoken to Alec yet, but if he's not fit to keep in the Test then he probably won't be fit to bat, either. "He's much more likely to get that finger hurt batting than keeping wicket."
Stewart has been used in a dual role throughout the series so far - a move that has allowed England to play five bowlers. But if he cannot play at Old Trafford, then the selectors may have to revert to either Steven Rhodes or Jack Russell - and give captain Atherton a new opening partner.
Jason Gallian would be the obvious candidate for that second role, but he too is missing this week's round of Championship matches because of a hand injury.Reuse content