The Cheltenham striker was poised to move to Sixfields to replace the outgoing Constantine but he failed to recover from the dead leg he sustained in the 2-0 win over Hartlepool, forcing Cobblers boss Stuart Gray to move
for Colchester's Scott Vernon.
The move worked out well for Northampton in the end, with Connor subsequently ruled out of Saturday's draw at Huddersfield and Vernon enjoying a goalscoring debut in the 4-0 victory over Stockport.
"I could have gone to Northampton with Leon coming this way, but I was struggling for Saturday and that was it," said Connor in the Gloucestershire Echo.
"They needed someone to come in straightaway, so it doesn't look like anything will be happening at the minute. I will have to stay and battle for my place here."