Dutch clubs had until 1st April to make a decision on the future of those who are running down their deals.
Mulenga is among those yet to commit to fresh terms and he may decide to move on at the end of the season.
The Zambia international, who boasts a prolific strike rate in the Eredivisie, was strongly linked with Nottingham Forest and Wigan Athletic last summer.
They may decide to rekindle their interest if the 30-year-old frontman becomes available.
Utrecht are refusing to give up on the possibility of Mulenga agreeing an extended stay with them, but acknowledge that they face an anxious wait as he weighs up all of his options.
They are also waiting to discover what former Swansea City midfielder Cedric van der Gun will decide to do next, as he is another prepared to take a risk on becoming a free agent.
Utrecht have, however, taken up the option of keeping Dave Bulthuis until 2016 and have wrapped up a permanent move for Willem Janssen - who had been on a season-long loan from FC Twente.