Lamar Jackson turned down a new contract worth around $250million due to a lack of fully guaranteed money, according to reports.

The Baltimore Ravens and quarterback Jackson ended negotiations for a long-term contract extension prior to Sunday's kick off of the new NFL season.  

Jackson will play for just over $23m on the fifth-year option of his rookie contract, having previously said he would not continue to negotiate during the season.

"Despite best effort on both sides, we were unable to reach a contract extension with Lamar Jackson," Ravens general manager Eric DeCosta said in a statement on Friday.

While talks will resume next offseason, NFL.com's Ian Rapoport reported on Sunday that while the offer to Jackson "eclipsed" the $242.5m one handed to Russell Wilson by the Denver Broncos earlier this year, "fully guaranteed money is believed to be at the heart of the issue".

Rapoport's sources also indicated the offer "fell short of the $230m, fully guaranteed deal that Browns quarterback Deshaun Watson received after Cleveland traded for Watson in March", and it is understood Watson's deal was the barometer used by Jackson in negotiations.

ESPN's Adam Schefter also reported on the deal, stating his sources believe Jackson turned down an offer worth around $250m.

The 2019 NFL MVP negotiated for himself with help from his mother and the NFL Players' Association, and the Ravens are expected to apply their franchise tag to prevent Jackson from hitting free agency if the sides are unable to reach a deal at the end of the season.

Even if no other quarterbacks sign lucrative deals in the meantime, exclusively tagging Jackson would cost the Ravens $45.4m in 2023 and $54.4m in 2024.

According to NFL reporter Chris Mortensen, Jackson rejected the offer of a six-year deal, with $133m fully guaranteed, more than Wilson's $124m and Kyler Murray's $103.3m with the Arizona Cardinals, though short by some way of Watson's $230m.

The Ravens kick off their season at the New York Jets on Sunday.