Cape Town - Paul Schoeman was due to play against the Blues in Auckland on Friday, but he was ruled out after his side's flight from Johannesburg to Sydney.
When the Cheetahs announced their team on Wednesday, Schoeman was sidelined with an "injury" and his place in the starting line-up went to Niell Jordaan.
Now, it has been confirmed by the Cheetahs that the real reason that Schoeman was ruled out of the clash was due to a scary run-in with thrombosis that developed on the flight.
A member of the Cheetahs management team currently in Auckland confirmed to Sport24 that Schoeman was "fine", but that he was still in hospital and that he would remain there for "as long as necessary".
The clots were found in his calf and, more seriously, in his lung.
As a result, Schoeman will not be able to travel for at least 14 days but, depending on how his recovery goes, he might have to stay put for up to a month.
It effectively rules the loose forward out of the rest of the Cheetahs' tour.
Following Friday's clash against the Blues, the Cheetahs travel to Wellington for a date with the Hurricanes and then to Tokyo to take on the Sunwolves a week after that.
Thrombosis occurs when a blood clot forms inside a blood vessel, causing problems in blood flow.
15 Melani Nanai, 14 Declan O’Donnell, 13 George Moala, 12 TJ Faiane, 11 Rieko Ioane, 10 Piers Francis, 9 Augustine Pulu, 8 Akira Ioane, 7 Blake Gibson, 6 Steven Luatua, 5 Scott Scrafton, 4 Patrick Tuipulotu, 3 Charlie Faumuina, 2 James Parsons (captain), 1 Pauliasi Manu
Substitutes: 16 Hame Faiva, 17 Alex Hodgman, 18 Ofa Tu’ungafasi, 19 Gerard Cowley-Tuioti, 20 Kara Pryor, 21 Sam Nock, 22 Ihaia West, 23 Michael Collins
15 Clayton Blommetjies, 14 Sergeal Petersen, 13 Francois Venter (captain), 12 William Small-Smith, 11 Raymond Rhule, 10 Fred Zeilinga, 9 Tian Meyer, 8 Henco Venter, 7 Oupa Mohoje, 6 Niell Jordaan, 5 Francois Uys, 4 Carl Wegner, 3 Tom Botha, 2 Torsten van Jaarsveld, 1 Charles Marais
Substitutes: 16 Elandre Huggett, 17 Ox Nche, 18 Johan Coetzee, 19 Armandt Koster, 20 Uzair Cassiem, 21 Shaun Venter, 22 Niel Marais, 23 Clinton Swart