The Germans will be represented at Easter Road to watch the Colombian international against Hibs tonight.
Eintracht were in Europa League action against Inter Milan last night, where they drew their last-16 first leg 0-0.
The German side currently sit fifth in their domestic league and are looking to make a final push to make the Champions League.
Coach Adi Hutter is well aware of the additional financial muscle that would give him if his team could make it through to Europe’s top tournament.
Hutter and his scouting team have been alerted to free-scoring Morelos and after watching extensive video footage.
They have now decided to step things up and watch him in the flesh.
Frankfurt paid £7million to make French striker Sebastien Haller their record signing from Utrecht two seasons ago.
But they would need to smash that to persuade Steven Gerrard to sell.
The German side are prepared to do that for the right players they feel can take them to the next level.
Morelos has been a major success in his two seasons at Rangers and has netted 28 goals in all competitions this term.
A string of top clubs have already been linked with Fenerbahce, Nice and Cardiff all credited with an interest in the 22-year-old over recent months.
Leicester – who are managed by ex-Celtic boss Brendan Rodgers – and Frankfurt’s German rivals Borussia Dortmund were this week reported to be interested.
Rangers have made it clear they will only sell if the price is right.
They value Morelos at around the same level as the £20m that Celtic got for Moussa Dembele from Lyon back in the summer.
The Light Blues turned down a £7m offer from Chinese club Beijing Renhe last January.
And they believe his value has increased now that he is a full Colombia international.
Morelos was signed by then-Rangers boss Pedro Caixinha from Finnish side HJK Helsinki in June 2017 for around £1m.