NEW YORK -- Heather Watson said she will undergo blood tests after suffering from breathing difficulties, back pain and a fever in her first-round loss at the US Open.
The British No. 2, who is now 0-6 in singles matches at Flushing Meadows, twice called for the trainer during her 6-2, 7-5 defeat to Richel Hogenkamp having felt unwell on another day of soaring temperatures at Flushing Meadows.
Watson had a medical timeout after losing the first set and cried in her courtside chair before taking medication and receiving treatment on her back. She later told reporters her symptoms felt "similar" to when she was diagnosed with glandular fever in 2013.
"It was horrible to play. I was just very ill," she said. "I've had a fever for the last three days but playing in this heat is almost impossible when you feel that bad. I was struggling to breathe and my back was just getting [sore].
"I don't really know exactly what it is but I've gone to see the doctor and I'm going to get some blood tests done and try and figure what it was."
Watson even needed one of the tournament doctors to carry her bag as she walked off Court 13.
The 24-year-old twice managed to battle back from a break down in the second set, and even had two set points to level the match, but Dutchwoman Hogenkamp managed to break Watson again for a chance to serve out the match.
Watson called for the trainer for the second time but wasn't able to take the second set to a tie-break, with Hogenkamp wrapping up victory in one hour, 42 minutes.
On Court 4, Daniel Evans joined fellow Britons Kyle Edmund and Johanna Konta in the second round here with a 6-2, 4-6, 7-5, 6-1 win over Rajeev Ram.
British No. 2 Evans, who made it to the third round here in 2013, next faces highly-rated German teenager Alexander Zverev.
The 26-year-old, now ranked 64th, entered the top 100 for the first time in May before making the third round at Wimbledon where he lost to Roger Federer.
"It was a bit patchy, could have been a bit more comfortable but winning first round is always good and in the end I was playing pretty well," Evans said. "It wasn't easy. It was a court where I struggle to concentrate quite a bit. It actually helped me in the end because I had to focus hard."
Later on Tuesday, Aljaz Bedene was unable to find a way past Nick Kyrgios, losing 6-4, 6-4, 6-4 on the Old Grandstand court.
Naomi Broady came out on top in a battle of Britain on Court 13 after edging Laura Robson 6-7(4), 6-3, 6-4.
Having been blighted by injury for long spells over the last tow years, Robson has enjoyed an encouraging run this summer with victory in an ITF tournament in Pennsylvania before she came through three rounds of qualifying in New York.
"I'm feeling a lot of things right now but mostly disappointed," the 22-year-old said. "I will get over it and probably think that overall this was a pretty good tournament but right now it sucks."