Miami Heat restricted free-agent guard Tyler Johnson signed a four-year, $50 million offer sheet with the Brooklyn Nets on Thursday morning, league sources told The Vertical.

The Heat have three days to match the terms on the sheet to retain him – or lose him to the Nets.

Tyler Johnson was undrafted coming out of Fresno State. (AP) More

The deal includes $18 million-plus and $19 million, plus "poison pill" provisions, in years three and four of the deal designed to severely puncture the Heat's salary cap and dissuade president Pat Riley from retaining Johnson.

Nevertheless, the departure of All-Star guard Dwyane Wade for a free-agent deal in Chicago late Wednesday could make the Heat more apt to match the sheet and retain Johnson.

For Johnson, the contract represents one of the most rapid financial ascensions in recent league history: from an undrafted NBA Development League guard in 2015, to participating in only 68 games over parts of the past two seasons, to a staggering market deal.

Johnson made $507,000 in his second NBA season for the Heat in 2015-16. He played 36 games – starting only five – but NBA executives and coaches who scouted him and studied him closely on tape in the D-League and NBA see the potential for a versatile and complete guard.

Johnson had a couple comparable offer sheets on the market, but the opportunity for playing time in Brooklyn, the chance to play for new coach Kenny Atkinson and under general manager Sean Marks, sold him on Brooklyn.

The Nets are signing unrestricted free-agent guard Jeremy Lin to a three-year, $36 million contract. Johnson was an undrafted free agent out of Fresno State in 2014. He missed nearly three months with shoulder surgery this season – only to return to play in the playoffs for Miami.