Article here about Fausto's season and the mononucleosis. It is all in Italian, but with some understanding of the language and some time watching the sport, should not be too difficult to understand a lot:
https://bici.pro/news/professionisti/quei-55-giorni-stop-non-scalfito-grinta-masnada/
Some key points:
-He already noticed signs of fatigue and struggling to recover at the UAE tour. He still went to Teide after that and to Catalunya but felt strange the whole time. After abandoning Catalunya he thought he had a bronchitis, but tests from the doctors revealed mononucleosis.
-In total, he had 55 days off the bike. Sometimes he tried to walk, but after 40 minutes couldn't continue due to fatigue.
-His first 1.5 hour training ride at the end of April felt like a victory
-He is currently training at Livigno with most of the Quickstep team. He will return to racing in San Sebastian, where he will probably work for Alaphilippe and Evenpoel, depending on how the legs are (he actually says he will 'respect the hierarchies'). Then he will lead the team at Vuelta a Burgos.
-The plan is to go the la Vuelta after that, but he is not absolutely sure yet whether he is selected (for me he would be 1st name at the teamsheet)
-He believes he has grown a lot as a rider since joining the world tour, but lacks the continuity and the opportunities to show exactly how capable he is. He he has wished to do 2 grand tours on the same year, to build the endurance, and says that only having 15 race day in July is a problem.
-Very grateful to the team for the faith they have and giving him time to look after himself.
Grande Fausto. To be one of the strongest in Suisse so soon after all this shows the grinta, the hard work, the character and the ability