The Wales outside-half admits confidence is high among the Red Dragons following back-to-back victories over England and Italy.
But France are unbeaten as well following their success over Scotland and then against England at Twickenham and that has alarm bells ringing for Sweeney.
He said: "I really don't think we have seen the best of this French team yet. You never quite know what you're going to get with France but you know that if they switch on, then they can beat any team in the world. That's the difficulty about preparing to play them.
"They have won two from two yet they have still taken some criticism from their supporters and the media. They are proud rugby people and are bound to react to that."
Sweeney, who won his 19th cap as a replacement against Italy, has been restricted in his time on the pitch by Stephen Jones but insists he is pushing his rival all the way.
He said: "I'm not here to make up the numbers. I'm pushing as hard as I can to get into the starting team but it's hard to force your way in with Stephen and the rest of the boys playing so well at the moment. But that's great news for Wales."
Principality Stadium will host the UEFA Champions League Final in six weeks' time. WRU chairman Gareth Davies, Football Association of Wales chief executive Jonathan Ford and Ambassador Ian Rush joined young sports fans at the trophy arrival at the venue to celebrate the magnitude of the event on Saturday 3rd June (kick-off 19.45).
British and Irish Lions captain Sam Warburton is looking forward to bringing together players from Ireland, Scotland, England and Wales for the biggest challenge of their careers - a series against world champions, New Zealand.
For the fifth year running, Wales referee Nigel Owens will be in charge of proceedings at Judgement Day V at Principality Stadium. It promises to be 'extra special' for the Wales' favourite ref, as he will be making his 150th appearance in the league.
There will be no shortage of inside knowledge from Bowl Finalists Caerphilly and Amman United when they face each other on Sunday at National Finals Day. Caerphilly hooker Rhys Cleverly knows the Principality Stadium pitch better than most as a matchday groundsman, while Amman United can look to Wales' record try scorer Shane Williams for some helpful advice.
Two hundred and 40 teams competed in the inaugural Urdd WRU 7s held at Pencoed last week with Welsh internationals Steff Andrews and Jasmine Joyce impressed with the talent on display, as was Urdd chief executive, Sioned Hughes.
The countdown is on for Judgement Day V as tickets for the big day at Principality Stadium soar through the 50,000 mark. Players and coaches alike are bursting at the seams to play in the double header with Dragons coach Kingsley Jones claiming there is a 'real buzz' about the event.
WRU TV went behind the scenes when the four regions got together to test their skill set for the BBC's Scrum V Live rugby show, at the WRU National Centre of Excellene in the build up to Judgement Day V. Blues' Matthew Morgan was one of the stars of the show while the Dragons' Cory Hill proved a surprise package...the full set of results will be revealed on tv screens on matchday
Wales assistant coach Richie Pugh is confident his side can cause a few headaches in the Hong Kong Sevens this weekend. In a tough group, Wales kick off their campaign against New Zealand on Friday before playing Japan and Fiji, who are chasing their third consecutive Hong Kong title, on Saturday.
Bedwas had to overcome a stubborn Carmarthen Quins side before winning the Foster's Challenge Cup final in Bridgend with a 23-18 victory. Bedwas captain Nicky Griffiths pays tribute to his side who have claimed the club's first piece of silverware in the modern era.
Team coach Brett Davey is aiming to keep his unbeaten run in cup finals at Principality Stadium intact when his side take on Amman United in the WRU Bowl final, after he guided Caerphilly to a 20-14 win against Cilfynydd in the semi-finals.
Penallta are hoping to go one step further than last season when falling to Bedlinog in the WRU Plate Final. After a titanic struggle against Nant Conwy, they have given themselves a great chance, after a hard fought 18-13 semi-final victory.