The defender only managed 36 minutes of football for Sunderland last season as he failed to break into Sam Allardyce’s side.
That saw him leave the club on loan in March, as he headed out to Championship side Bristol City in search of game time to try to ensure a place in Wales' squad for Euro 2016.
He made it into the provisional squad, but was cut from the final 23-man selection by manager Chris Coleman.
And Brown has admitted that he did feel sorry for his former teammate missing out on a place in the summer showpiece.
“I feel a bit for Adam Matthews who sadly didn’t make the squad. That’s life, that’s football but I still feel for him and I wish him all the best,” he told celticfc.net.
It will now be interesting to see if Matthews has a role to play at Sunderland next season under Allardyce.
The Black Cats boss is expected to be very busy in this summer transfer window as he looks to improve the squad and ensure they are not fighting relegation again.
If last season is anything to go by he does not have a place in the first-team squad and where he could end up remains to be seen.