Widely recognised as one of the best defenders outside of the First Division, Thomas made his full international debut in a 0–0 draw with Northern Ireland in 1967 – he remains the club's most capped international footballer.
Thomas is widely regarded as one of the top defenders outside of the top division, and his debut in a 0–0 tie against Northern Ireland in 1967 marked an important milestone – he remains the club's most capped international player to this day.