Names of Mahajan and two leaders were recommended by the state unit of the Congress to its national committee for selection, he said.
The election for six seats from Maharashtra will be held on March 23.
Presently, the Congress and the NCP each hold two of these six seats while the BJP and Shiv Sena share the remaining.
Vandana Chavan and DP Tripath of the NCP, Rajani Patil and Rajiv Shukla of the Congress, Ajay Kumar Sancheti of the BJP and Anil Desai of the Shiv Sena will retire on April 2.
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"Mahajan is one of the three probables whose names have been recommended to Delhi. The rest of the two names are not yet declared but one of them could be Rajiv Shukla who is already a sitting member of the Upper House," he said.
According to the leader, former Union home minister and Sonia Gandhi loyalist Sushilkumar Shinde could be another probable.
"We have given three names. However, the party could nominate someone else as well," he said.
Mahajan, a socialist leader who joined the Congress along with Babanrao Pachpute of the Janata Dal in early 1990s, had left it in 1999 and switched allegiance to Sharad Pawar-led NCP.
The BJP, with 122 MLAs, can win three seats with the help of Independents while the Sena (63), the NCP (41) can win one seat each.
The notification for the polls would be issued on March 5 and the last date for filing nominations would be March 12.
The last date of withdrawing nominations would be March 15 and elections, if necessary, would be held on March 23.