Senior shares fell after Bloomberg reported it was preparing to reject the latest bid proposal from Lone Star Funds as too low.
The US private equity firm said on Monday it had made a fifth and final approach to Senior worth 200p a share in cash. The proposal valued the engineering group at about £839m.
Bloomberg said Senior could announce as early as Tuesday that it had rejected the approach. Discussions are continuing and Senior could change its mind based on discussions with its leading investors, Bloomberg said.
Lone Star said on Monday the latest proposal was its final offer and would not be increased unless a rival bidder emerges. Senior has rejected four previous bids from the firm, including an offer of 185p a share earlier in June.
Senior shares fell as much as 12% and were down 9.4% to 150.10p at 08:34 BST.
