Chris Froome has won the Tour de France four times, but Welshman Thomas continues to improve with the years and sits higher up in the overall on the first rest day, just 43 seconds off the yellow jersey and 59 seconds ahead of Froome
"I think it's early to be talking about that," Thomas said about any disputes over leadership between him and Froome.
"Maybe if I'm still right there after Alpe d'Huez [on stage 12], it's a bit different then. But we haven't even done a proper climb yet. I'm certainly not getting carried away."
Thomas led the race for four days in 2017 after winning the opening time trial in Düsseldorf. However he was forced to abandon due to a crash in stage nine.
Nether Thomas nor Froome have shown any signs of discontent such as those that surfaced in 2012 when Froome was deployed as a domestique to Bradley Wiggins but was capable of dropping his team leader on the climbs.
"We've spoken in general about things," Thomas said. "He's keen for me to try… if I do have the chance to stay up there, to let me have that. But we're honest with each other."
Watch: Tour de France stage nine highlights
Out of the next three days, the Alpe d'Huez stage on Thursday should have "the biggest selection" in the overall classification. Team Sky take decisions about who will be their leading GC contender after that stage and before the race reaches the Pyrenees.
"I don't think so," Thomas said of any potential inner-team rivalry. "Hopefully we'll be the last two guys anyway, and we ride the same as a team up until that point anyway. And then you go from there.
"But I don't think so at all. I've ridden with Froomey for a number of years now and we can certainly be honest with each other, and not lie about how we're feeling, to get one of us to ride for the other one. It should be all right."
For his part Froome said the 2018 Tour is "a totally different situation" to 2012 when he and Wiggins seemed to clash on the road.
"He [Thomas] is riding extremely well and it just puts us in an even better place," Froome said.
"I think the race, as always, will decide [who leads]. For us it's fantastic to have different cards to play. Movistar have come here with three leading riders, and with only one GC contender it becomes difficult to cover all three.
"If you look at all the GC riders, G is right up there. It's for other teams to attack us now."
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