Johnson, a key figure in the rise of Welsh rugby over the last 18 months, has been linked with the Australian head coaching vacancy and a future opening at Premiership club Leicester.
The Wallabies are looking to replace Eddie Jones, who was sacked after Australia's 24-22 defeat to Wales last month, while Leicester need to find a successor for Pat Howard, who returns Down Under at the end of the current season.
Johnson has not signed a contract with Wales so he is technically free to walk away at any point.
There is little danger of him jumping ship before Wales launch the defence of their RBS 6 Nations title - but Ruddock is aware he needs to act swiftly to persuade Johnson his future lies in Wales.
"We need to know sooner rather than later," said Ruddock.
"I had a chat with him on Tuesday and I will be sitting down and talking to him about it. I look forward to catching up with him this week and getting into a bit of detail.
"I can see why he is being chased from many quarters. He is a brilliant coach.
"He is totally focused on the Six Nations, that is where his mindset is and he certainly hasn't indicated to me he is ready to move on.
"He is his own man and we respect that. However long it takes to wait, we will wait and the message is: We want Scott Johnson in Wales.
Johnson has had a major input in producing the high-tempo, exhilarating style of rugby Wales have played with such great success over the last 18 months.
He has been at the heart of a side which rose from the ashes of a 10-match losing run under Steve Hansen to the glory of last season's Grand Slam and a rare victory over Australia last month.
Ruddock added: "If he did go, we'd have to find two guys to replace him. One to help coach the backs and another to help rally the troops on match day.
"The real quality of his work is the fact he went through 10 games with the Welsh team when they got beaten. He stuck in there, he helped the guys improve their skills and come out of the bad times and help mould them into a great attacking team.
"All if have done is say: 'I like the look of how we played that game, let's keep that going and make it better'. His work is there to be seen."