Schleck saw the race off on stage four from his home town in Mondorf-les-Bains, Luxembourg. The peloton raced the stage back into France towards Vittel.
"It's up there," Schleck told Cycling Weekly. He pointed to his house just above the start village and then turned his attention back to the peloton and the favourites.
"With [Alejandro] Valverde's crash and abandon, the race is now back in team Sky's favour. Unfortunately, Geraint is in the wrong team because he's the guy who can beat Froome," he said.
"Porte is extremely strong, but every one knows that and is watching him very closely. Sky is watching him. Who is left? Aru and Fuglsang."
Perhaps fans could see a situation like 2012 with Bradley Wiggins and Chris Froome, where the team helper is just as strong, if maybe stronger, than the captain.
"I don't say that, but if the was a team who just supported him, like Movistar, he'd be a real threat for Froome," Schleck added.
"Yeah [it would have been good to see Thomas change teams]. I'm happy for the team, I admire Thomas and Froome is a great champion and a friend.
"I wanted to see Thomas have a chance. I know, he re-signed, but that's a choice you have to make in life."
Schleck says the race swings in Sky's favour because they have the true two-pronged approach with Froome and Thomas.
"Honestly, it looks like Sky did everything right. Next to Froome and Sky, I think there's one team that can beat them, Astana. They have two cards to play with Fabio Aru and Jakob Fuglsang.
"Movistar has no Valverde. Before, Valverde was my favourite. To win the overall? Yeah, I observed him in the Tour of Catalonia and País Vasco. Normally he would be dropped on the very long climbs, but now he managed to drop the others.
"He managed to really step up. We only have three uphill finishes and Valverde is only weak in the high altitude, which was only two stages this year. He was my pick. I believe many experts would agree with me."
Followers will have their first understanding of the race's strongest riders with stage five, the 5.9km summit finish to La Planche des Belles Filles on Wednesday.
"It is very early in the Tour," said Schleck. "You still have a long way to the Alps and Pyrenees, but on the other hand, you can still say you have the yellow jersey on your shoulders. But if you want to win, maybe [stage five] is not the day."
Schleck took the 2010 Tour title after Alberto Contador lost the title due to a doping positive. He retried in 2014 after suffering injury in a crash on the way to London on the third stage of that year's Tour.
At 32 - the same age as Froome and just a year older than Thomas - Schleck now owns a bike shop and works for Tour organiser ASO at select races.
"I feel very honoured to be here," Schleck said.
"I made all the rounds with the television stations, seeing the journalists and old friends, but on the other hand, I'm happy to be retired. I'm very busy, I have a very full schedule every day. I miss it a little bit yes.."
"I'm in the shop every day, but I'm also president of the Tour of Luxembourg, so that's a big thing for us to organise, and I do eight events for ASO, so much in the Asian countries, but also in London and South Africa, where they do L'Étape du Tour."
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