The Australian, 28, is out of contract at the end of this year, with seats potentially open at top teams Mercedes and Ferrari next season.
McLaren want to keep lead driver Fernando Alonso in 2019, but he has not decided whether he wants to stay in F1.
The Spanish two-time world champion, 36, is likely to race in the Indianapolis 500 again next year.
Alonso is believed to be weighing up whether to race Indy in addition to the F1 programme – but skipping the Monaco Grand Prix, which clashes, as he did last year – or taking on a full season in Indycars.
McLaren’s prime option is to keep Alonso in F1 but, should he leave, the team are looking for a driver as a replacement who is as close to the two-time champion’s level of ability as possible.
Ricciardo, as a seven-time grands prix winner regarded as one of the best drivers on the grid, fits the bill.
Alonso has said he will not make up his mind on his future until mid-summer, but has said he finds the predictability of F1 “sad”. Only three teams – Mercedes, Ferrari and Red Bull – have won a race in the past five years.
Alonso won the Le Mans 24 Hours last weekend, the second of two legs of the unofficial ‘triple crown’ of motorsport that he has now completed.
Already a Monaco GP winner, that leaves only the Indy 500 for him to become only the second driver in history after Graham Hill to win all three events.
Alonso said on Thursday before this weekend’s French Grand Prix: “One thing we need to wait and see a couple of months now is really the commitment of all the parties into the F1 project and to the future, what will be the seats that next year move on, and which will be the driver line-ups of some of the top teams as well.
“After that, let’s see what the future brings, whether it be the Indy 500, triple crown or whatever seems attractive. At the moment I am enjoying Le Mans and not taking too much into account next year.”
A McLaren spokesman said: “We never comment on driver matters.”
McLaren are considering setting up an Indycar team in 2019, most likely in partnership with an existing leading outfit.
Chief executive officer Zak Brown has said their analysis is still ongoing but that conditions are looking “favourable”.
