"Unfortunately I think the three of us will be out of it," Thomas said, adding that countrymen and Sky teammates Luke Rowe and Owain Doull would also miss theGoldCoast games.
"Where they fall in April is the wrong time for us. Luke and Owain will still have the cobblestone classics in Belgium, which will be their main target. At the end of the day, Team Sky pay us to race bikes for them and we've got to do what they say. Especially as it's in Australia, it's not like you can fly in and out over a weekend."
Thomas won gold in the 2014 road race ahead of Jack Bauer and Scott Thwaites, days after winning bronze in the time trial.
"In cycling you hardly get a chance to race for Wales so every chance you do get is amazing and you want to make the most of it," added Thomas who has won two Olympic Games gold medals in the team pursuit. "To come away with two medals and win the road race was unbelievable, and something I'll always consider one of my biggest victories."
The road race events at the Commonwealth Games are due to take place on April 10 and 14 in 2018, clashing with the cobbled classics such as Paris-Roubaix.
Jan Bakelants to start 2017 season at the Tour Down Under
Belgian Jan Bakelants has told Sporzathat he will start his 2017 season in Australia with AG2R-La Mondiale, lining up at the Tour Down Under. Having finished third at La Méditerranéenne, eighth overall at La Provence, ninth at Classic Sud Ardèche and second in the Drôme Classic to start his season, Bakelants is hoping for a similarly good start to his season at the WorldTour race.
"My season starts in Australia, where I will start with ambition in the Tour Down Under. I have ridden well there in the past and hope to do it again. Last year I was a good start to the season, but that was smaller races (in France, ed) that what remained outside attention," he said. "I would also like to ride Strade Bianche and Milan-Sanremo."
With the Tour of Flanders starting close to his home in Antwerp, Bakelants is also hoping to add the Belgian monument to his schedule.
Romain Lemarchand signs for Delko Marseille Provence KTM
Lemarchand, 29, has previously ridden for AG2R La Mondiale and Cofidis, Solutions Crédits and brings substantial experience to the team.
The team has also signed Ángel Madrazo (Caja Rural-Seguros RGA), Mauro Finetto (Unieuro–Wilier), John Anderson Rodriguez (EPM-UNE-Area Metropolitana), and Gatis Smukulis (Astana).
Mirko Selvaggi announces retirement
Italian Mirko Selvaggi has taken to Facebook to announce his retirement at the age of 31 with no contract extension forthcoming from Androni Giocattoli - Sidermec. Selvaggi turned professional in 2008 with Cycle Collstrop, before riding with Astana and Vacansoleil - DCM in the WorldTour. Prior to joining Androni for the 2016 season, he spent two seasons with Wanty - Groupe Gobert.
Although Selvaggi never won a race in his career, he rode the Giro d'Italia in 2011 and in 2012, helped teammate Thomas De Gendt to third place overall.