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.
The 6ft 2ins defender was signed from Cannes four years ago but never appeared in the 2008 FA Cup winners' first team.