Yann Nsaku, a former youth teamer with Portsmouth, has been arrested in France as a "suspected islamic terrorist plotting anti-semitic attacks".
Suspected radical Jeremy Sidney, who apparently groomed Nsaku, was shot in the head and killed by French police after a shootout in Strasbourg.
Authorities said the group aimed to spark a Muslim “war across France"
Nsaku, 19, was with Pompey's youth team until last year when a knee injury ended his career and he returned to France.
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The 6ft 2ins defender was signed from Cannes four years ago but never appeared in the 2008 FA Cup winners' first team.