A week before the NFL fully opens the free agency floodgates, the Oakland Raiders locked up punter Marquette King to a long-term deal and now the rebuilding franchise is reportedly focused squarely on securing veteran left tackle Donald Penn.

Keeping one of the cornerstones of their offensive line may be a challenge, even for a team with the third-most salary cap space heading into free agency. NFL Network’s Ian Rapoport reported Penn is expected to be in heavy demand this offseason.

An unrestricted free agent Penn went undrafted out of Utah State in 2006 before signing with Tampa Bay. The 32-year-old wound up in Oakland in 2014 on a two-year deal, leads a top-heavy 2016 free-agent class at tackle.

Penn’s an attractive commodity to any number of teams both due to his success on the field, durability, and his contract history. In 2015, Oakland’s cap took only a $5.4 million hit on Penn’s contract and he has started 128 consecutive games since 2008.

However, with Buffalo placing the franchise tag on Cody Glenn, Penn’s value on the open market will increase and puts pressure on Raiders general manager Reggie McKenzie to have a deal in place before free agency officially opens on Monday.

NFL teams are allowed to contact players’ agents at that time, though no deal can be signed until Wednesday, per NFL rules. Still, that does leave more than two days for another team to either outbid the Raiders or woo Penn out of the Bay Area.

Penn is part of an interesting class of linemen, including some Pro Bowlers, but he stands out as potentially the best deal of the bunch. Chicago already let Jermon Bushrod go, as did the New York Giants with William Beatty, while Seattle will have to deal with self-represented Russell Okung.

All three of those tackles made between $7 million and $8 million last season, and each likely expects a pay raise. Whereas Penn would be cheaper given a raise for him falls in line with their previous wages.

The Raiders can also ill-afford to lose a player as important as Penn while quarterback Derek Carr continues to develop after his best season as a pro. Oakland’s frontline allowed only 33 sacks last season, ranking No. 11 in the NFL, with Penn, and young guards Gabe Jackson and J’Marcus Webb the only lineman to start every game.

King, meanwhile, joined a long and historic list of Raiders specialists when his new deal was announced Monday. The terms of the deal have not been released.

“It feels real good, man,” King told reporters during a conference call. “I’ve actually done more and more research on how the Raiders have handled their specialists and stuff and how good they are. It feels good to be a part of that.”

King, 27, himself an undrafted free agent out of Fort Valley State, proved to be one of the NFL’s best punters last season. He ranked second in the league with 40 punts inside the 20-yard line, which also broke the franchise record of 33 set by Shane Lechler in 2008. The Raiders are also famous for drafting Ray Guy, arguably the greatest punter in NFL history.