Millwall snatched a late 1-1 draw at already-relegated Leicester on Friday to move back into the Championship's automatic promotion places but missed the chance to put pressure on Ipswich.
Substitute Macaulay Langstaff's first goal since February cancelled out a Foxes opener from Harry Souttar, who was playing his first game since rupturing an Achilles 16 months ago.
It moved Alex Neil's visitors up to second, a point ahead of Ipswich, but the Tractor Boys now have two games in hand.
Ipswich play at West Brom on Saturday and Southampton on Tuesday so Millwall must hope automatic promotion is still a possibility when they finish their season at home to Oxford next Saturday.
Souttar broke the deadlock in the 78th minute, bundling home after a cross from Luke Thomas.
Millwall needed a response and substitute Langstaff provided it in the final minute.
Ryan Leonard's flick found the forward in space in the box and he lashed past Jakub Stolarczyk.
Frank Lampard's Coventry have already secured promotion to the Premier League.