Chelsea interim manager Guus Hiddink says attacking midfielder Pedro could miss key games for the club after suffering a hamstring injury against Southampton.
The Spain international joins defender John Terry and striker Radamel Falcao on the sidelines.
Striker Pato could make his club debut this week but he is expected to only be on the bench tonight against the Canaries.
"I will see Pedro now, yesterday he was here for treatment," Hiddink told reporters.
"Normally with these injuries I'm not that positive that it will be resolved in a few days but I need the information from my medical staff.
"John [Terry] is touching the pitch with some running and we'll see how he reacts after training this week.
"I'm a bit cautious because with these injuries there is a danger of setbacks. Regardless of age you must be very careful.
"If there is a game [to aid his recovery] it will just be a six-a-side or seven-a-side, not a big game, an intense small game.
"Pato is eager and there is healthy competition among the strikers with Diego as number one, it's a very good atmosphere.
"The others have stepped up and I'm happy with the progress of Bertrand Traore.
"He's not ready for 90 minutes but he's ready to play part of the game. That's why I said in his situation the best thing was to have him on loan, so he could get used to the club and the club could make a proper judgement on his performances.
"We have to be careful with some players that they're not going over the top with their physical load."