The Tinkoff-Saxo General Manager thinks Contador is in the best form that he has seen him in since he signed the Spaniard in 2011.
But Riis admits Froome is still the favourite even though Contador has ridden well in the last few months.
The Spaniard finished the Tour de France in fourth place last year but didn't manage to challenge the Brit at all as Team Sky dominated the overall race.
The 31-year-old only had one win during last season and this came when he won a stage of the Tour de San Luis.
However this season the Tinkoff-Saxo rider has impressed and looks to be back to his best.
According to Cycling News, Riis said: "I think he's reached a good level. There's been a lot of hard work and it's been nice to follow.
"There’s a lot of determination and I’m happy to see him back to that level. I think this is the best I’ve seen him since he came to the team. It’s hard to compare but he’s definitely strong.”
“Some years are good, and some years are less good. He had some tough years but he’s had a good winter and has a good programme. For us it’s just important that he’s at a good level and that he’s up there where we want to see him.”
Contador is set to do battle with Froome once again this year as he looks to stop Team Sky winning three successive tours.
Riis believes he is one of the favourites but there are plenty of riders who can win it.
He said: “He was among the favourites last year and he’s going to be among them this year."
“Froome obviously the big favourite and the man to beat, there’s no doubt about that but there will be some other guys. Valverde is doing good.”
For Riis Contador's best performance this year was in Paris Vasco where he finished second in an individual time trial, seven seconds off World Champion Tony Martin.
“It was important to see the one he did in Pais Vasco. That was crucial for him, mentally, that he was up there and really strong. That has maybe been the most important thing this year because he needed that, to show to himself that he could do it.”
With the likes of Froome and even Bradley Wiggins having excellent time trialling skills, Contador will have to be on the top of his game to not lose any time to the Sky riders.
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