Big hitter Lance Klusener is rated just 50-50 to start the Steelbacks' Twenty20 Cup campaign against Warwickshire Bears at Wantage Road tonight.
The South African has a minor tear in a muscle in his back and will be given a fitness test today to decide if he will be able to make his Twenty20 debut for the County.
Klusener has had a superb start to his Northants career, and is the club's leading batter in the four-day and one-day competitions.
It would be major blow for Northants to lose the 34-year-old for a Twenty20 Cup, which the club felt at the start of the season they had a good chance of winning, especially with Klusener in the side.
Physio Barry Goudriaan said: "It is only a minor tear, but he is feeling some discomfort and is probably 50-50 for tomorrow's game.
"We are working on him and will probably decide on him today. We had him doing a workout in the warm-up before the game at Trent Bridge yesterday but it is still touch and go for tomorrow."
Klusener missed Sunday's two-wicket defeat against Notts, which brought to an end Northamptonshire's miserable C&G Trophy campaign with the Steelbacks finishing bottom of the North Conference with just one win to their name.
Director of cricket Kepler Wessels refused to talk after the defeat, and his problems will not have been helped by Klusener's injury on top of Steven Crook's back problem.
The young all-rounder is still feeling pain in his back, which has now been diagnosed with a problem with a disc.
Goudriaan said: "Steven is very frustrated because he wants to play.
"We gave him an epidural in his back, but that has not worked. The specialist says it just needs rest, so in another two or three weeks we will build him up slowly again."
New signing Sourav Ganguly was also struggling in the field with a thigh problem yesterday, although he did manage to bowl and Goudriaan says he will be able to make his home debut against Bears tomorrow night after hitting his first half-century for the club.