Jim Mallinder confirmed George Pisi pulled his hamstring in a bizarre incident in Saturday’s Champions Cup defeat to Racing Metro.
Pisi broke free of the Racing backline, only to lose his grip of the ball and fall to the ground having sustained the injury.
It cost Saints, who were 10-6 down at the time, the chance to get into the lead for the first time in the game and they went on to concede a late try and lose 20-11.
Mallinder confirmed that Pisi had sustained a problem metres from the line and is now hoping for a positive diagnosis.
“He pulled his hamstring,” said the Saints boss. “It just went as he was running.
“We’ve just got to hope that it’s not bad and it doesn’t keep him out of the game for too long, but he’ll be a little bit sore.”
Phil Dowson’s 75th-minute score had seemingly made up for the Pisi disappointment, but Stephen Myler’s missed conversion was to cost Saints dear.
Racing pounced on a Ben Foden clearance attempt late on, with Marc Andreu scoring and Johannes Goosen converting to deny the away side a losing bonus point.
And Mallinder said: “That’s one of the disappointing things, that you work hard all week, you come out here, you’re in bonus-point territory throughout the game, you have a chance to equalise and to lose it at the death it disappointing.
“Not getting a bonus point is not the best.
“We said they would tire, we saw signs of that in the first half and in the second we got on top. If we’d have scored that (Pisi) try it would have made the difference.”