Chelsea manager Guus Hiddink says Alexandre Pato is in the midst of a personal pre-season and will not be selected until he is fully fit.
The Brazil international moved to Stamford Bridge on loan for the remainder of the season from Corinthians last month after his previous temporary spell at Sao Paulo ended in December.
Former Milan striker Pato has not played competitive football since late November and Hiddink says the 26-year-old remains some weeks off his Chelsea debut.
"Pato is in his pre-season. We have made a training plan which he is doing now, training at least once but most of the days twice, which means he is getting his fitness but not full fitness yet," he said, ahead of Sunday's Premier League game against Manchester United.
"He will not be in for the upcoming few games because we want to have him fit because we don't want the risk of injury in this tough league.
"Of course we know he is skilful, technically he is very good and he is ambitious, of course. This is normal for me but he needs more physical fitness.
"He played his last game in November then had a holiday because it is a different season. So this is kind of a pre-season for him. We like to pressure him but we must be careful not to go over the top."
Pato was one of Brazil's most promising talents prior to joining Milan in 2007 but, after a positive start to life in Italy, he returned to Brazil following a string of injuries.
Interim boss Hiddink has previously encouraged Pato to make the most of his chance with Chelsea and reiterated the positives of the loan move.
"It is good to have him on loan and not in a situation where the club has offered him a longer term," the Dutchman added.
"It's good for both parties. They can see whether they fit well with each other."