Arsenal manager Arsene Wenger feels loan deals should be treated just like permanent transfers.
Fabricio Coloccini has re-affirmed his commitment to Newcastle amid fresh speculation that he wants to leave.
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.