The midfielder's contract with Spartak Moscow was ended by mutual consent last month.
Shirokov started out at CSKA but has spent most of his career with Zenit St Petersburg where he won the Russian Premier League title twice and the UEFA Cup in 2008.
The 34-year-old has scored 13 goals in 52 games for Russia.
CSKA are top of the league with 37 points from 18 games.
(Reporting by Dmitriy Rogovitskiy; Editing by Tony Jimenez)
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