Tests have now confirmed a thigh strain for Coutinho, so the Inter starlet could well be out until 2011.
The Brazilian pulled up during training on Friday morning “after a challenge with a teammate” in the game between ranks.
He was taken in for tests, which have confirmed “a femoral bicep strain in the right leg,” according to the official club website.
Although the statement does not state the extent of the damage or how long a lay-off is required, the prognosis is not good.
Coutinho is likely to be out for anything from four weeks to two months, so his 2010 could well be over.
It rules him out of the Club World Cup to be played in Dubai in December.
There are 11 players missing for Sunday's trip to Chievo, most of them with muscular problems.
The absentee list now includes Douglas Maicon, MacDonald Mariga, Diego Milito, Thiago Motta, Sulley Muntari, Joel Obi and Walter Samuel.
Goalkeeper Julio Cesar is also a doubt for tomorrow's Serie A match, again due to a muscular injury.