A Bill Ackman protégé is angling to fight Zayo Group Holdings after the company rejected a $6 billion-plus offer in the last few days from the Blackstone Group, sources told The Post.

Former Pershing Square investor Scott Ferguson, chief of Sachem Head Capital Management, which he launched in 2014, has written recent letters to Zayo CEO Dan Caruso urging him to sell the company, three sources said.

Boulder, Colo.-based Zayo makes communications infrastructure, with networks throughout the US and Europe.

Blackstone made a binding offer in the last few days for Zayo at around $30 a share, after conducting due diligence, sources said.

The new offer is a bit lower than the non-binding offer Blackstone made weeks before.

Zayo has indicated it is rejecting the offer, sources said.

Shares of Zayo fell 3 percent Monday, to $25.51, after trade publication CTFN reported that Blackstone had made an offer weeks ago of about $30 a share, less than what the market expected.

Sachem has a reported 2 percent stake in Zayo.

If Sachem launches a proxy fight, it may not be easy.

Zayo has a staggered board, with three directors coming up for election in what will likely be a November annual meeting, sources said.

Sachem last had activist success when it pushed the Premier Inn chain to consider selling its Costa coffee chain, which was eventually sold to Coca-Cola.

Blackstone and Sachem declined comment.