Diego Costa has failed to find the net for three games running.
The Brazilian-born Spain international traded Atletico Madrid for Chelsea in the summer and began Premier League life with a bang, notching seven goals in his first four league matches.
The goals continued to flow for the 26-year-old as the Blues consequently stormed to the top of the table and embarked on a 14-game unbeaten run.
Costa, however, has long battled against a succession of hamstring problems, and he has been restricted over the last eight weeks to just a handful of appearances.
Since netting in the comfortable 2-0 victory over West Brom, the former Atletico Madrid man has fired blanks in the subsequent three matches, a run Mourinho puts down to a lack of match sharpness.
“The problem isn’t goals because they’ll come as a consequence of his condition. He was injured and a long time without training and that obviously must have an effect,” he was quoted as saying by The Sun. “So he must recover, but there’s no big problem.”
Costa has fired in 11 Premier League goals in 1007 minutes of league action overall this season, a scoring rate of one goal per 91 minutes.
Despite his terrific start, he was soon overtaken by Manchester City striker Sergio Aguero in the top scoring charts as the Argentine sits at the top with 14 goals.