Brown said Roulston had been "peeing a lot and didn't drink enough and had severe dehydration.
"He's gutted for his team and for his sponsors who have supported him so well,'' Brown added.
Roulston's father, Brian, who is the manager of his strong Calder Stewart team in this year's tour, said: "He's a bit dejected at the moment but he'll live to fight another battle.
"He was devastated because he thought he had the legs and everything like that to achieve winning it five times. But there's another year next year.''
Brian Roulston said safeguarding his son's international career was a priority following his signing with pro team Radio Shack Nissan Trek.
"It's more than just the Tour, his health is more important than anything else.'' Brian Roulston said.
Hayden Roulston has a history of medical problems. A heart condition forced a temporary retirement in 2006 but he fought back and won silver in the road race at the
Commonwealth Games in Delhi last year to go with his Olympic silver and bronze medals on the track in Beijing in 2008.
Brown said the treatment for his latest condition was to simply wait for the stones to pass naturally, a process Roulston wasn't looking forward to.
He didn't think it would affect Roulston meeting up with his new Radio Shack Nissan Trek team as scheduled early in the New Year.
As Roulston was transported by ambulance to hospital for scans, news the race lead was up for grabs filtered quickly through the peloton and teams scrambled to adjust their tactics.
And it was Christchurch 19-year-old Josh Atkins who took advantage when powering up the 3km final Crown Range climb to take a memorable victory.
Atkins, who rides internationally for Lance Armstrong's powerful Trek-LIVESTRONG team, said: "It's good to finally get a stage win for PowerNet ... that's all we wanted so we got that and I got the yellow,'' he said.
"I didn't really come into the Tour with too many goals. It was a last-minute decision and for a while I was regretting coming down.
The climb wasn't without its unexpected challenges.
"I got ridden into the back of the wheel so my derailleur was pretty banged up so I was riding the whole climb with my gears chopping and changing. The Tour is never without drama.''
He now boasts a 1min 9sec lead over Ascot Park Hotel's Patrick Bevin, of Rotorua, with Kia Motors' George Bennett, of Nelson, a further 16sec back. The trio also hold the top three placings in the battle for the under-23 jersey.
Atkins was confident the PowerNet team could successfully defend the yellow on tomorrow's 167km stage from Invercargill to Gore.
"My legs are getting better and better each day so I'm not feeling too worried about tomorrow. If the wind's blowing, I know the guys will have me at the front and I know I can ride there all day,'' he said.
He predicted Saturday's penultimate stage featuring the individual time trial at Winton could define the race.
"I've won numerous national (time trial) titles so I think I'll go all right.''
Results from Stage 5 of the PowerNet Tour of Southland.
Te Anau - Five Rivers - Kingston - Frankton - Crown Range
1. Josh Atkins (PNT) 4h22m06s; 2. Patrick Bevin (APH) at 29s; 3. Jeremy Yates (STR) at 29s; 4. George Bennett (KMT) at 35s; 5. Andi Bajc (STH) at 39s; 6. Taylor Gunman (OWA) at 51s; 7. Mike Olheiser (JPW) at 55s; 8. Brendan Sharratt (CSL) at 01m01s; 9. Scott Lyttle (PBR) at 01m06s; 10. Brett Tivers (STR) at 01m10s; 11. Tim Gudsell (PBR) at 01m16s; 12. Chris Macic (STR) at 01m20s; 13. Aaron Strong (APH) at 01m22s; 14. Eric Drower (PTL) at 01m33s; 15. Alexander Ray (OWA) at 01m41s; 16. Dion Smith (OWA) at 01m41s; 17. Joseph Cooper (MCP) at 01m46s; 18. Shem Rodger (PBR) at 01m55s; 19. Paul Odlin (SUB) at 01m55s; 20. Westley Gough (SUB) at 01m59s; 21. Danny Pulbrook (RDS) at 02m07s; 22. Marc Ryan (CST) at 02m30s; 23. Clinton Avery (APH) at 02m30s; 24. Simon Binney (SIT) at 02m35s; 25. Tom Scully (PNT) at 02m38s;
Overall Standings
1. Josh Atkins (PNT) 15h35m17s; 2. Patrick Bevin (APH) at 01m09s; 3. George Bennett (KMT) at 01m25s; 4. Chris Macic (STR) at 01m26s; 5. Jeremy Yates (STR) at 01m28s; 6. Scott Lyttle (PBR) at 01m30s; 7. Andi Bajc (STH) at 01m38s; 8. Mike Olheiser (JPW) at 02m19s; 9. Tim Gudsell (PBR) at 02m21s; 10. Paul Odlin (SUB) at 02m22s; 11. Taylor Gunman (OWA) at 02m32s; 12. Shem Rodger (PBR) at 02m35s; 13. Brett Tivers (STR) at 03m00s; 14. Dion Smith (OWA) at 03m15s; 15. Joseph Cooper (MCP) at 03m27s; 16. Westley Gough (SUB) at 03m44s; 17. Marc Ryan (CST) at
03m45s; 18. Nick Lovegrove (SUB) at 04m00s; 19. Clinton Avery (APH) at 04m09s; 20. Danny Pulbrook (RDS) at 04m15s; 21. Tom Scully (PNT) at 04m40s; 22. Peter Latham (SUB) at 05m06s; 23. Simon Binney (SIT) at 05m45s; 24. Ryan Obst (RDS) at 07m39s; 25. Greg Taylor (UHM) at 08m19s.