McCague missed Kent's last game against Hampshire with a back problem but had a net yesterday and coach John Wright and captain Steve Marsh will monitor his reaction.
Graham Cowdrey is also troubled by a similar problem so Kent have put Matthew Walker on stand-by as cover.
Gloucestershire will leave out opener Nick Trainor, who has failed to score in seven innings this season. He will be replaced by Dominic Hewson, a 22-year-old right-hand batsman from Cheltenham.
Glamorgan, the other joint leaders, will make a late decision on whether to call up batsman Michael Powell or seamer Darren Thomas for their match against Surrey at The Oval.
Matthew Maynard, the Glamorgan captain, will look at the pitch before making his decision. The former England batsman is backing his spin partnership of Robert Croft and Dean Cosker to get the better of Surrey's Saqlain Mushtaq and Ian Salisbury. "Saqlain is a magician," said Maynard. "He's a wonderful spin bowler and Ian has proved that if it is his day he can also be a match-winner. But we have match-winning spinners of our own."
Fourth-placed Yorkshire are set to retain an unchanged side against Worcestershire at Headingley. Their veteran seamer, Peter Hartley, recovering after a hernia operation, bowled two overs in the 10-over Sunday clash with Lancashire at Old Trafford but may not be fit enough for a four-day match .
Worcestershire captain Tom Moody is set to continue as an opener and name an unchanged side. Tim Curtis, who retires at the end of the season, is again omitted as Worcestershire aim to bounce back after defeat by Middlesex.
Somerset's off-spinner Harvey Trump is to retire at the end of the season due to a niggling back injury. Trump, 28, made his Somerset debut in 1988 and has taken 243 first-class wickets, including a best of 7 for 52, achieved twice in the same game against Gloucestershire at Gloucester in 1992.
Surrey's Ben Hollioake has won the Cricket Writers' Club Young Cricketer of the Year award.Reuse content