Gordon is RFA at the end of this season. Even the 1st-round tender amount is only $4.15M - the equivalent of a 1-year "prove it" deal.
It seems unlikely to me that Gordon would hold out for more. And, it sees a near certainty that no other team would be willing to beat the tender amount with an offer that the Browns would deem prohibitive, AND give the Browns a 2018 1st-round pick should the Browns decline to match. Gordon doesn't really have any options of his own (aside from retiring) until 2019.
If Gordon stays clean and performs near to his perceived capabilities in 2018, then he may have a market in 2019. Gordon will be 27 next April and 28 in April 2019. A team that has recently acquired a franchise QB and is 1-2 pieces away from challenging for a SB berth, AND has lots of cap space with which to take a risk, may ge him one big 3-4 year contract at that point - assuming that the Browns haven't successfully extended him or franchised him by then.