Darren Clarke is facing a race against time to be fit to play in the Masters.
The Open champion limped off the course at the Houston Open on Friday, having strained a groin muscle during his second round of 71.
Clarke felt the injury while completing his rain-delayed first round on Friday morning but played on through the pain barrier to complete his second round.
"I wanted to keep going as I need to play all four rounds before the Masters," said Clarke.
Clarke's second round of 71 put him one under for the tournament and he missed the cut by one shot.
Graeme McDowell completed his second round on Saturday and his 69 left him on five under and seven behind leader Jeff Maggert.
Padraig Harrington squeezed into the final two rounds on two under after a 73.
Clarke earned a five-year Augusta National exemption in winning last year's Open championship and he will be competing in the event for the first time since 2007, when he missed the cut.
On completion of his second round in Houston, it was suggested by Clarke's personal trainer that he attend a local doctor to assess the full extent of his injury, but he declined.
"I've had these type of injuries in the past and there's not much you can do but rest," Clarke insisted.
"It's a really long walk around this golf course and I could have come in after three to four holes this morning. It seemed okay when I finished my first round today but it just got progressively worse in the second round," he said.
At the end of day two in Houston, England's Brian Davis had a share of the lead alongside Louis Oosthuizen of South Africa on 11 under.