Westwood missed the cut when the Open was last played at St Andrews in 2005
World number three Lee Westwood was able to take part in the French Open as a swelling in his calf that was first feared to be a blood clot subsided.
The 37-year-old missed Wednesday's pro-am suffering from swelling in his calf and ankle but doctors assured him it was probably a reaction to the heat.
"It was just a check," Westwood said. "It will need a bit of physio, it is probably age more than anything."
Ian Poulter, Colin Montgomerie and Matteo Manassero were also fit to play.
Westwood was third in the Open at Turnberry in 2009 and is regarded as one of the favourites to secure his first major title when the Championship begins at St Andrews on 16 July.
He was also third at last year's US PGA Championship and at this year's Masters went one better, finishing second behind Phil Mickelson.
Westwood then won the St Jude Classic before claiming a share of 16th place in the US Open at Pebble Beach.
Explaining the background to the injury scare Cage added: "Lee felt pain in the calf and it was swollen on Tuesday. But when he woke on Wednesday his ankle was swollen too so he decided to have it checked out in the physio's truck.
"The French doctor there thought it could be a blood clot and said Lee should got hospital for tests so he pulled out of the pro-am."
Poulter, meanwhile, had an unpleasant experience when an insect bite sustained during practice at Woburn became infected and resulted in a lump in his groin, but the 34-year-old world number eight declared himself fit to start.
Ryder Cup captain Montgomerie has been suffering from a calf strain for several weeks but with the aid of painkilling injections was able to tee up on Thursday.
And 17-year-old Italian Manassero was able to honour his invitation despite being hit on the hand by a wayward ball during practice earlier in the week.