Transfer news: Striker Samuel Eto'o has left Everton and joined Italian Serie A side Sampdoria on a two-and-a-half-year deal
Samuel Eto'o has completed his move from Everton to Sampdoria, signing a two-and-a-half-year deal.
Kiernan had a temporary spell at Griffin Park in November, making seven appearances for Uwe Rosler's side before returning to the Latics.
The Republic of Ireland Under-21 international featured in both central defence and midfield and played a key role in Brentford's win over Sheffield United in late November, helping to set up the first goal.
He is available for selection for the Bees' League One game at Oldham on Saturday.