Robinson, who on Friday completed the signing of defender Charles Dunne, confirmed Well recently rejected a Jambos bid for 20-year-old Cadden.
"The offer that was made was verging on laughable for someone of Chris's talent," Robinson said.
"The offer of £100,000? We will move on very quickly because it won't be something I will consider."
Scotland under-21 international Cadden has made 69 appearances for the Steelmen after making his debut in 2014, netting seven goals.
"It's football, isn't it?" Robinson added. "The other teams will try to get your players for as cheap as they can and we will try and sell them for as much as we can.
"But it doesn't warrant a discussion. Chris is a big, big part of our plans. He is one of the best young players in Scotland and there will be interest in him, no doubt.
"Chris's time will come when he will probably leave but it won't be for that kind of money and it won't be at this time.
"Chris isn't someone who is wanting to leave the club and race away anywhere else. His development is here, he will get better and better at our place.
"But it is a little bit frustrating when some of the perceived bigger clubs think they can come in and unsettle your players."
Well, meanwhile, confirmed the signing of former Blackpool and Oldham defender Dunne on a one-year deal.
The 24-year-old former Republic of Ireland under-21 international worked under Robinson at Oldham.
"We haven't seen the best of him yet as he's had a bit of a stop-start time with injury and he just needs to play football, so we are delighted to have him," the Motherwell manager said.
"He's strong, quick, and good in the air. He's definitely getting back to that form and he just needs someone to believe in him.
"I do need another right-sided centre-back/right-back, so we'll assess them after the games."
French defenders Cedric Kipre, a 20-year-old former Leicester player, and Bira Dembele, a 29-year-old former Barnet player, could feature as trialists for Motherwell in a friendly at Stirling Albion on Saturday alongside former Barnsley striker Shaun Tuton.
Motherwell are also understood to have made an enquiry about Peterborough striker Shaq Coulthirst, although any move would depend on other forwards leaving.
Motherwell boss Steve Robinson says Hearts' bid for midfielder Chris Cadden was far too low to be taken seriously.