The number of players whose deals expire in June runs into double figures at Rovers, while James Coppinger is to retire.
One player has committed his future to the club, with winger Jon Taylor, currently sidelined with an ankle injury for the rest of the season, signing a new three-year deal.
Players whose futures remain up in the air include Joe Wright, Reece James, Brad Halliday, Madger Gomes, Jason Lokilo, AJ Greaves and Danny Amos.
Butler said: “I am sure a few players are thinking who the next manager is going to be, whether it is myself or someone else. It is important who is in charge and maybe that is playing on their minds.
“But I will say in these unprecedented times that (with) contracts and players, a lot of players will be out of contract in this close season and if you want to take your chances with the amount of players who are free agents, it is their choice and they have got to back themselves.”
On ex-Rotherham United wingman Taylor’s decision to sign fresh terms, Butler, whose side visit ex-Rovers manager Darren Ferguson’s Peterborough on Tuesday night - with an eye on spoiling their planned promotion party - added: “I am really pleased. Tayls is a great part of the squad and asset to the team when he is fully fit. His running statistics proved how vital he is to the team and his pace and directness is always an outlet for us. I am really pleased for John to get it over the line.
“John epitomises everything we are trying to do. With his all-round community work as well comes hand in hand with everything Club Doncaster are trying to do and it is important you get the right people in and around the club.
“John is a good lad and great professional and hopefully he rubs off on the others. On his day, he is a match for any League One defender.”
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