The Coventry striker has made just four substitute appearances for the Sky Blues this term having battled with his weight and fitness.
Three of those have come since manager Andy Thorn deemed Eastwood surplus to requirements at the Ricoh Arena back in October, although the 28-year-old has remained on the periphery all season.
Eastwood's four-year contract with Coventry is due to expire in the summer and a positive impact for the Shrimpers as they battle for promotion from League Two over their remaining eight games of the campaign could lead to a possible permanent switch.
The former Wales international first joined Southend in November 2004 after a prolific brief loan spell and went on to enjoy huge success at Roots Hall - scoring 63 goals in 134 appearances - before clinching a big-money move to Wolves in 2007.
Eastwood told Southend's official website: "I can't wait to put a shirt back on, it's been a while. I've not been playing at Coventry recently and I'm desperate to come back and score the goals we need to get Southend promoted."
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