Costa had a disappointing campaign last season but is back to his best under the leadership of Antonio Conte, firing home 10 goals as the Blues have marched to the top of the Premier League table.
His form has not gone unnoticed elsewhere and reports are rife that Inter are ready to test Chelsea's resolve by launching a mammoth bid at the end of the season.
This time last year, Costa looked to be heading for the exit door as he struggled for form, but the Blues will do all they can to rebuff all interest.
Reports are rife that Chelsea will offer the Spain international a bumper new contract and he could be tempted to sign it as Chelsea continue to flourish.
Real Madrid and Atletico Madrid are also keen but Chelsea will have no intention of cashing in on the strike ace.