Doubt has been poured on the theory that paint sprayed on the pitch at the Stadio Olimpico caused Lazio striker Giuseppe Sculli to have an allergic reaction.
The 29-year-old scored a rare brace of goals early in the first half against Palermo on Sunday, but had to go off after the interval when his skin started to swell and turn red.
Lazio doctor Roberto Bianchini revealed he had given Sculli an anti-histamine injection at half-time, but to no avail and Edy Reja had to use a substitution.
Initially, it was thought that the paint used to colour up the barren parts of the pitch was to blame, but the same substance was used at Marassi where Sculli played with Genoa for four years.
However, doctors are not ruling it out. After all, allergies can lay dormant for year and a lone incident is enough to set one off.
Sculli will undergo a series of tests this week to establish the cause and hopes to be available again for the derby on Sunday.