Andy Murray was forced to pull out of his doubles match alongside brother Jamie at the Monte Carlo Masters.
|Andy Murray (right) was in action with his older brother|
The world number 10 struggled during the first set against Poles Mariusz Fyrstenberg and Marcin Matkowski.
The Scottish pair lost a first set tie-break before Murray, 19, withdrew with a back injury.
Murray is due to meet Marc Giquel in the second round of the singles event on Tuesday but may not be fit enough to play the Frenchman.
He said: "I hit a shot and my back went into spasms and got worse and worse after every game. I'll have to see how it feels in the morning."
A month ago, the Scot was well beaten in the Indian Wells Masters semi-finals after suffering a hip injury in the previous round.
Murray moved to 10th in the world rankings on Monday after Tommy Haas failed to reach the US Clay Court Championships semi-finals.