Chelsea will kick off their English Premier League title defense against Swansea on Saturday, but they could play without star striker Diego Costa.

Chelsea boss Jose Mourinho told reporters that he is still unsure if Costa, who was their leading scorer last season, will recover in time for their Premier League opener.

Mourinho said that Costa started feeling hamstring pain after their game against FC Barcelona in Washington last week. The 26-year-old striker was feeling well in training camp before their Community Shield game, but Costa also failed to play, leading to a 1-0 loss to Arsenal on Sunday.

"Will Costa be fit for Swansea? I don't know," Mourinho said. "You think I'm lying, but I'm not. Two days ago he was ready to play and yesterday he trained normal. He had a little problem after the Barcelona game. After that he was training normally and we thought he would be ready, but then he was feeling uncomfortable."

Mourinho consciously tried to give his players enough rest to keep themselves fresh for their title defense, but the trick did not work for Costa, who is still being bothered by his recurring hamstring issues.

Costa, who moved from Atletico Madrid to Chelsea before the start of last season, appeared in just 24 Premier League games for the Blues last season, but he managed to score 20 goals.

Mourinho, whose team is considered favorite to repeat this season despite improvements made by Manchester City and Manchester United, knows they need a healthy Diego Costa to defend keep the title in Chelsea.

Baba Rahman Moving to Chelsea Soon?

Meanwhile, Chelsea might add another defender to their roster before the start of their campaign.

ESPN FC reported that the Blues are nearing a deal to acquire Baba Rahman from Augsburg, who acquired the left-back from Greuther Furth for €2.5 million last year.

Rahman was supposed to play for Augsburg on Saturday, but was eventually pulled out of the lineup, citing muscular problems. Augsburg coach Markus Weinzierl said, though, that the transfer talks affected Rahman.

Mourinho has been looking for defensive help after Filipe Luis decided to return to Spanish La Liga powerhouse club Atletico Madrid. Branislav Ivanovic, Kurt Zouma, Gary Cahill, Cesar Azpilicueta and John Terry headline their defensive lineup, but Mourinho said that five defenders will not be enough.

"Five is not enough. That's obvious," Mourinho said. "We cannot go to the Premier League with five defenders. That's our weakness. The quality is good, but the numbers are not enough."