The Kansas City Chiefs will play the San Francisco 49ers on Sunday in a massive clash in Week 5 of the NFL regular season. Both teams are on 2-2, but both recovered from slumps with impressive wins last week. Neither will want to go back on the slide again, but only one of these teams can leave Levi's Stadium in Santa Clara today with the win.

The game can be watched on the CBS network at 4.25 p.m. EST, or online through live stream on Direct TV's NFL Sunday Ticket by clicking here.

The 49ers impressed last week by becoming the first team to defeat the Philadelphia Eagles this season. A strong second half saw them come back from a 13-21 deficit at half time to claim a morale-boosting 26-21 victory.

However, the Chiefs were also in fantastic form in Week 4. On Monday Night Football, Kansas City wiped the floor with the New England Patriots, winning every single quarter comfortably to claim a massive 41-14 win. If they can continue that same form here tonight then the 49ers will have to be at their absolute best to steal the win away from them.

Today's game comes amid news that the NFL will begin on Monday to test players for human growth hormone (HGH).

Earlier in September, the NFL and the NFLPA announced that they had agreed to a new drug policy; that new agreement was widespread but included HGH testing for the first time in the NFL's history.

A letter written by NFLPA president Eric Winston to players has been leaked, and was published on NFL.com.

The letter reads: "As you know, the new Performance Enhancing Substances Policy includes HGH testing. Testing for HGH will begin on Monday, October 6th.

"Each week of the season, 5 players on 8 teams will be tested. No testing will occur on game days. We negotiated to ensure that the methodology of testing be conducted in the most professional and safest manner for players.

"Importantly, after three years of negotiating, players won the right to challenge any aspect of the science behind the HGH isoforms test in an appeal of a positive test."

If any performance enhancing drug policy violations are found, including HGH, the case will then be passed onto and handled by an independent arbitrator.