The Eagles have had two players on the injury list for "illness," one of whom (Jernigan) was still out yesterday. Very likely flu (or the roughly equivalent adenovirus that is also making the rounds this year - the latter is usually confined to institutions like army bases).
This virus might be adding to ‘flu’ misery, but you can't get the vaccine
Either of these can do real damage to a team. Being strong and healthy sometimes doesn't help against the flu - indeed in the 1918 flu epidemic that killed more people the first World War, it was the folks in their mid-20's that were most vulnerable.