Mohun Bagan were dealt a blow following the injury to defender Dhanachandra Singh who was playing for Chennaiyin FC in the ISL.
Dhanachandra played for Mohun Bagan in the last I-League.
The left-back has been ruled out for the season and remains doubtful for the I-League starting January 7 next year.
In order to shore up the rear guard, Mohun Bagan coach Sanjoy Sen is said to be looking at Rocha, 34, known simply as Ruben who started his footballing career in Spanish heavyweight Real Madrid's youth academy.
After a handful of appearances with Real's senior team and loan spells with Borussia Monchengladbach in Germany as well as with Albacete in Spain, Ruben made a switch to Racing Santander in 2006.
The veteran centre-back has also played for Celta de Vigo, RCD Mallorca, Osasuna and Real Zaragoza in Spain and FC Baku in the Azerbaijan Premier League.