Thomas got to within 20 seconds of the leader's yellow jersey
Team Sky principal Dave Brailsford says Cardiff's Geraint Thomas is capable of winning cycling's great races, but his 2010 Tour de France effort will fade.
"There's nothing to suggest he won't be a very good general classification man on grand tours," he told The Back Page.
Thomas, 24, was within 20 seconds of the leader's yellow jersey on Friday before the first mountain challenge.
He was dropped from the peloton on Saturday's seventh stage and left in 31st place with tough tests to come.
In the middle of the day - with Fabian Cancellara dropped from the peloton - Thomas had been in the provisional yellow jersey position, but a puncture, and punishing inclines saw the Welshman lose over five minutes on the lead group.
To [have been] sitting second in the Tour de France, you don't do that every way, do you?
On Sunday he dropped a further 25 minutes on the leaders, leaving him in 69th overall.
"Nobody should get too excited [about Thomas in the 2010 Tour]," Brailsford told BBC Radio Wales' Saturday morning radio programme.
"He won't be able to hold the same pace as the pure mountain leaders and will drop away from the top of the leaderboard over time.
"It's a question of him assuming his role and helping [Team Sky leader] Bradley Wiggins, doing everything he can to help him in his quest for the general classification."
Thomas wore the white jersey for the best young rider from his second-placed finish over the cobbles on stage three until Saturday when Andy Schleck took over.
Thomas' primary 2010 Tour role is to support Bradley Wiggins
"To [have been] sitting second in the Tour de France, you don't do that every way, do you?," said Thomas.
"It's nice and it's been good, especially wearing the white jersey for a few days.
"I didn't even dream of that, I was focused on helping Brad, so it's a really nice bonus."
The 97th Tour is the second for Thomas, who is part of the first British team to compete since 1987.
The British Road Race champion finished 140th in 2007, nearly four hours behind winner Alberto Contador, becoming the first Welshman in 40 years to finish the gruelling race.
Wales is also represented in Team Sky by British Cycling's performance director Brailsford and former Wales coach Shane Sutton.
He's probably more suited to one of the one-day classics, but... he's learning all the time and gaining experience
Dave Brailsford on Thomas
"There may have been surprise at home about the way Thomas has performed, but there's no surprise in the team," Brailsford told The Back Page.
"He's worked with us for several years since he was a young lad, he's a very, very talented athlete.
"His focus so far has been on the track, but now he's had a block of time to focus on the road.
"He's got a very good sprint and on undulating, low hills he's very strong.
Brailsford is one of three Welshmen with key roles in Team Sky
"He's probably more suited to one of the one-day classics, but... he's learning all the time and gaining experience.
"It's very much open to see how he develops over the next couple of years and gets the most out of his career."
The 20-stage Tour covers 3,642km (2,263 miles) before finishing in Paris.
"You should expect the climbers to come through [now we're in the Alps]," said Brailsford.
"That will give us a clue to what is to come in the Pyrenees in the last week."