I'm unaware of any formal offer, but the world knows how Daniel Levy works (Real Madrid as much as anyone), and there were claims in the media as early as 2016 that Real were interested, but put off by the price tag on numerous occasions (at one time, rumored at over £200m). Real were still linked with him last summer, and may have put in an offer of £40m for him, with Levy countering with £80m. It was expected my several media outlets that Real Madrid would offer £60m, and Levy would let him go at that price, but it seems Real never made that final offer.
Barcelona were also rumored as interested in 2017-18, but Spurs were unwilling to sell. I've linked a couple of sources below, but these are by no means the only ones.
TOTTENHAM will refuse to sell Christian Eriksen to Barcelona this summer, according to reports.
www.express.co.uk
Christian Eriksen's agent hints at a move, Mauricio Pochettino emerges as Real Madrid's target, Joachim Low turns them down, and William Carvalho is available.
www.eurosport.com