The 28-year-old will complete the temporary switch to Tannadice subject to international clearance.
The forward won a move to Brentford in 2012 after netting 28 goals in the Scottish First Division with Falkirk.
El Alagui managed just three goals in 12 appearances during an injury-hit first year with the Bees before managing six strikes in 18 games so far this campaign.
- Sports & Recreation
- Scottish First Division
- El Alagui