The 27-year-old has agreed a two-and-a-half year contract with the English Premiership leaders and will give manager José Mourinho another option in midfield following Scott Parker's metatarsal injury. However, Jarošik will not be eligible for the UEFA Champions League, having played in the competition already this season with CSKA.
The former AC Sparta Praha player spent two seasons with CSKA, helping them win the Russian Premier League in 2003. Now his goal is to help Chelsea secure their first league title in 50 years and he said: "I hope I will become an important part of the squad and help Chelsea to achieve their goals for the season. It's a great challenge for me and I'm really looking forward to the opportunity."
©UEFA.com 1998-2016. All rights reserved.