Danny Willett admits he is yet to fully recover from an illness ahead of the 145th Open at Royal Troon.
Masters champion Willett played 11 holes at the course on Monday, but has revealed his preparation has been far from perfect.
The Englishman has enjoyed only one top-20 finish since his triumph at Augusta in April, finishing third at the BMW PGA Championship in May.
"I was a bit sick last week but I am getting round the back of that and went out and played a few holes today," Willett told Sky Sports.
"Hopefully I can get another good night's sleep and get out there and have another good round on Tuesday.
"We're getting there but I was pretty bad for a couple of days. I'm just getting back on top of everything really, getting the fluids back in and hopefully getting back to full fitness by Thursday.
"It's going to be good playing with them to see where you are at in comparison, and see what they do. I'm relatively new to being around this all the time so it's interesting to see what they do differently. We've got another two days to get a plan together for the golf course and then play our own game."
Willett will partner world number one Jason Day and Rickie Fowler in the opening two rounds in an eye-catching group on Thursday and Friday.
The 28-year-old described the conditions as "brutal" following his practice on Monday, and he expects a fierce competition.
"I played 11 holes today and it was nice – fun and interesting," he added.
"Visually it doesn't seem as difficult as what I think it plays. You knock it into a couple of the bunkers you are not supposed to be in and you have to come out sideways.
"We played the last five straight into the wind and that was pretty brutal, but it will all be weather dependant, like most Opens are, and I think it's going to be a fantastic test."
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