Mohun Bagan suffered their first loss in 10 matches in the I-League when Churchill won 2-1 at Vasco in the last round exposing their defensive woes.
Eduardo Ferreira and Anas Edathodika were not able to gel as a centre-back combination as the Goans under Derick Pereira won their second match in three outings.
"Our lack of communication in the backline is a cause for worry. We need to rectify that. I have pointed it out categorically to my players," coach Sanjoy Sen said.
Mohun Bagan's star forward Sony Norde will look to score early as the Haitian conceded their rivals East Bengal are already in an advantageous position.
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"Yes, they have the advantage but the league is still open. We are in a good position and we cannot lose any more points if we have set our aim on the title," Norde said.
With two matches in hand, Mohun Bagan occupy third place in the table as they would look return to winning ways against the struggling Mumbai FC.
"We did not get time to build the team. We just had three days before the first match as most players came from ISL. We won the first two matches but I knew in the long run it would be tough," coach Santosh Kashyap said.
Mumbai will be missing their Brazilian midfielder Alex Willian who is down with a groin injury.